Small-Signal Stability Analysis of Three-Level Grid-Connected Inverters Using Hybrid H-Matrix Modeling

This paper proposes and verifies a generalized stability criterion for AC power systems composed of grid-connected inverters. A hybrid H-matrix modeling approach is applied to represent the dynamic behavior of both three-level DNPC inverters and AC bus networks in the dq coordinate system. Stability analysis is conducted through transfer function derivation and return difference matrix formulation. The proposed criterion is assessed using both frequency-domain techniques (including Nyquist and Bode plots) and time-domain simulations in MATLAB/Simulink, under different settings of PI parameters within the inner loop. Simulation outcomes verify its capability in distinguishing between stable and unstable system states. Additionally, experiments reveal that overly increasing that PI parameters can undermine system stability, emphasizing the importance of appropriate controller tuning in inverter-dominated AC networks.