Complex Frequency-Based Control for Inverter-Based Resources

This paper proposes a novel control scheme for inverter-based resources (IBRs) based on the complex frequency (CF) concept. The control objective is to maintain a constant CF of voltage at the terminals of IBR by adjusting its current reference. This current is imposed based on the well-known power flow equation, the dynamics of which are calculated through estimating the CFs for the voltages of adjacent buses. The performance is evaluated by analyzing the local variations in frequency and voltage magnitude, as well as the frequency of center of inertia (CoI), and then compared with conventional frequency droop, proportional-integral (PI) voltage controllers, and virtual inertia. The case study utilizes a modified version of WSCC 9-bus system and a 1479-bus model of the Irish transmission grid and considers various contingencies and sensitivities such as the impact of current limiters, delays, noise, R/X ratio, and electromagnetic transient (EMT) dynamics. Results show that the proposed control scheme consistently outperforms the conventional controllers, leading to significant improvements in the overall dynamic response of the system.