Frequency Stability of Renewable Energy Integrated Low-Inertia Power Systems During Grid Faults

In low-inertia power systems, frequency stability during the grid fault is in immediate danger. Increasing application of inverter-based generations (IBGs), the dynamics of which are determined by the control strategy, has reshaped the frequency nature of the synchronous generator-dominated power system. In this regard, this paper proposes a holistic Synchronization–Based Frequency model to describe the frequency dynamics of the low-inertia power system during the grid fault. The model captures the system’s synchronization dynamics that exert a considerable impact on the frequency stability. Based on the model, new mechanisms for frequency stability are revealed. Firstly, synchronization stability is found to be necessary for frequency stability in renewable-rich power systems. Secondly, the power balance between the total active power generation and total active power demand determines the frequency dynamics. The singular perturbation method is used for the steady-state analysis. A new form of frequency instability is found. The power balance-restricted frequency stability curve gradually approaches the synchronization stability boundary as the fault gets more severe, and eventually exceeds the boundary. The system suffers from frequency instability as no equilibrium point for power balance exists within the synchronization stability region. Simulations are conducted in SIMULINK to verify the correctness of findings.