Impact of variable renewable energy sources on the power system frequency stability and system inertia

Achieving net-zero emissions in line with the Paris Accord necessitates significantly increasing VRES deployment. This study investigates the impact of VRES integration on power system transient stability, extending beyond frequency response to examine synchronous machine rotor angles and system inertia. A novel contribution of this study lies in its systematic exploration of the nonlinear dynamics of power systems, comprehensively investigating the impact of VRES integration on power system stability, focusing on frequency response and rotor angle dynamics. As inertia declines due to VRES integration findings reveal a concerning trend of deteriorating frequency response. This trend suggests a likelihood of frequency instability at high VRES penetration levels, which could trigger the activation of grid protection relay mechanisms. When integrated within permissible limits, VRES can enhance system stabilization, however, this study reveals a trade-off: while VRES integration improves frequency response, it introduces less coherent and more oscillatory machine behavior, underscoring a limit on VRES penetration for maintaining stability. A critical VRES penetration threshold of approximately 44 % was identified, beyond which the system faces heightened risks of instability. Exceeding this threshold introduces significant challenges, including faster RoCoF, lower frequency nadirs, extended response times, and an elevated risk of protection relay activations, such as UFLS and RoCoF mechanisms. It is imperative to manage VRES integration to prevent instability carefully. To address this, "virtual inertia" is proposed to compensate for the diminishing inertial response of traditional generators. Techniques such as FFR, battery energy storage systems, and supercapacitors are recommended for further research and integration. This holistic approach is essential for maximizing VRES penetration while ensuring grid stability. The insights gained from this study can inform policy decisions, grid planning, and the development of control strategies to optimize VRES integration while ensuring grid stability and compliance with grid codes. This study has been implemented on an IEEE14 bus system using Siemens PTI PSS/E software.