Active power control of the photovoltaic (PV) power generation system is a promising solution to regulate frequency fluctuation in a power system with high penetration of renewable energy. This paper proposes an autonomous active power control of a small-scale PV system for supporting the inertial response of synchronous generators and load-frequency control. In the proposed control approach, an effective grid frequency regulation scheme is realized using slow and fast frequency response characteristics. A low pass filter-based frequency measurement is used for slow frequency response characteristic, while direct frequency measurement is used for fast frequency response characteristic. The designed dual droop characteristics-based control is shaped to achieve a smooth transition between slow and fast response modes. The performance of the proposed control strategy is demonstrated for serious disturbance scenarios, i.e., considerable power-load imbalance and generation trip. In the load-power imbalance test scenario, the proposed control works properly within the normal frequency deviation region and even when the frequency deviation exceeds that region occasionally. In the generation trip test, the frequency deviation is mitigated quickly, and the employed droop control is smoothly transferred from the slow response mode to the fast response mode.
