A Current-Scaling Strategy for Droop-Controlled Grid-Forming Inverters in Off-Grid Systems

Abstract

The progressive replacement of synchronous generation by inverter-based renewable energy resources is altering the dynamical structure of modern power systems, reducing system strength due to the inertia curtailment. In this context, grid-forming inverters have emerged as a fundamental technology capable of establishing voltage and frequency in inverter-dominated grids. However, their effective deployment is intrinsically dependent on the control framework that must guarantee stability, robustness, and interoperability under complex and uncertain operating conditions. The most adopted grid-forming control strategy is droop control. This work presents a proportional scaling strategy in the inner current loop for droop-controlled grid-forming inverters, which preserves the current angle, reducing only its magnitude if a large disturbance occurs. Moreover, an innovative grid-forming controller parametrization procedure based on hybrid jellyfish search and particle swarm optimizer is also provided. This methodology avoids empirical tuning and allows incorporating system constraints in the controller tuning procedure. Hardware-in-the-loop results demonstrate high performance of the optimized droop under nominal operation, load variation, black-start, and faults.