Time-Varying Equivalent Power Source Modeling for High Penetration Renewable-Rich Grids

The output responses of renewable energy sources differ significantly from those of a synchronous generator during disturbances. Therefore, an accurate and adaptable equivalent model is urgently needed for power system analysis in modern renewable-rich grids, such as in short-circuit current calculations and transient stability simulations. First, a model that accounts for time-varying characteristics in quasi-steady states is established, and a stepwise algorithm is proposed accordingly. The proposed model can provide power system operators with clearer information on the system operating status, and it can also provide updated data support for online short-circuit calculations, transient simulations, and voltage stability analysis. Then, a composite power source model including both synchronous generators and inverter-based resources is established, and a corresponding parameter identification method is developed. Finally, the proposed model and method are applied to the transient simulation of a power system. The model’s initial state is updated before a disturbance occurs, based on tracking results. The differences between curves obtained from the stepwise algorithm and benchmark simulation curves are compared and analyzed, both before and after a characteristic change in the time-varying power source. The effectiveness of the method is verified through simulation cases in Simulink and PSASP, respectively. It is shown that the proposed approach improves the accuracy of online transient simulations and thereby enhances the safety and stability of the power system.