Performance Analysis for LFC of an Enhanced IEEE 9-Bus Power System with GFL and GFM Inverter Control

The paradigm change for electrical power generation is inevitable due to more and more integration of renewable energy sources (RESs) into the utility grid. The consequence of such integration poses challenges in maintaining the frequency and voltage stability of the power grid. The majority of grid-tied inverters function in grid-following (GFL) mode, regulating their output through a phase-locked loop. GFL inverters are unable to directly regulate voltage and frequency, their ability to offer auxiliary services to the grid is comparatively limited. The limitation of GFL inverters led to the research in grid-forming (GFM) control techniques and they offer functionalities similar to synchronous generators. GFM inverters actively regulate their frequency output, which enables them to naturally support the system frequency while sharing a portion of the load variation. The present work studies and compares the effect of GFL and GFM inverter control at various penetration levels in providing frequency support for an enhanced IEEE 9-bus system. This enhanced IEEE 9-Bus system emulates a two-area interconnected load frequency control (LFC) system. The presented LFC model comprises a synchronous generator-based conventional thermal, inertia-less inverter-based solar energy and electric vehicle, developed and simulated in MATLAB Simulink® environment, for analysis. The virtual-synchronous-generator control mechanism of the GFM inverter and the droop-control mechanism of the GFL inverter are implemented in this work. The magnetotactic bacteria optimization (MBO) technique is used to fine-tune the PID controller gains of the LFC, GFL, GFM loops, and network parameters respectively of the presented system model. The enhanced IEEE 9-Bus system model is validated against the standard IEEE 9-Bus system and the stability analysis is further examined under various inverter penetration levels. Simulation results show that compared to GFL inverters, the high penetration of GFM inverters improves the power system frequency stability. 1