Distributed Event-Triggered Hierarchical Control of PV Inverters to Provide Multi-Time Scale Frequency Response for AC Microgrid

With the increasing penetration of inverter-interfaced photovoltaic (PV) systems in AC microgrids, the system inertia is increasingly deficient and the frequency response ancillary service provided by PV systems will be inevitable. In this paper, in order to make the PV systems provide multi-time scale frequency response, a novel distributed event-triggered hierarchical control (DEHC) of PV inverters is proposed, which includes a primary frequency response (PFR) control loop and a secondary frequency response (SFR) control loop. For the PFR, the PV inverters that operate in frequency regulation (FR) mode can arrest the frequency deviation in sub-seconds time-scale by an automatic deloading strategy, which is with low cost and easy to implement as no requirements for a storage system, irradiance sensors, and MPP estimators. For the SFR, the PV inverters that operate in FR mode can respond to the reference instruction assigned by a high-level AGC control center in seconds time-scale based on a novel distributed control strategy, which can converge within a fixed-time that independents to the initial conditions of the system. Furthermore, a novel event-triggered mechanism is designed to reduce the communication costs between PV inverters. Finally, case study results verify the effectiveness and improved performance of the proposed method.