Lab-based implementation and verification of new LFSM requirements in state-of-the-art grid-following inverters

This paper investigates the feasibility of implementing the newly proposed PRNB (grid security-based primary control) require-ments in state-of-the-art grid-following inverters. While current LFSM (Limited Frequency Sensitive Mode) specifications primarily define static droop characteristics, they lack stringent dynamic performance criteria. With the increasing share of inverter-based generation and decreasing system inertia, faster and more predictable frequency response is essential for grid stability. A laboratory-based test bench was developed to evaluate the dynamic response of a commercially available 6 kVA PV inverter under both existing VDE-AR-N4105:2018 guidelines and the proposed PRNB requirements. Using a real-time simulator and systematic parameter variation, the inverter’s frequency-dependent active power response was measured and calibrated against PRNB boundary curves. Results show that the tested inverter significantly outperforms current LFSM requirements and, after parameter optimization, can meet the tightened PRNB dynamic specifications without compromising stability. These findings confirm the technical feasibility of PRNB-compliant behaviour in existing hardware and provide a basis for refining future grid connection standards.