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Abstract With the explosive growth of photovoltaic (PV) penetration, there is an increasingly urgent expectation for PV sources to provide a full range of ancillary services to the utility. The most critical issue for a PV source to support the power system is the flexible power regulating capability, whereas the PV sources generally operates in the maximum power point tracking (MPPT) mode to maximize the solar harvest. This paper proposes an active power control strategy for PV sources based on a characteristic curve fitting method. With the proposed control strategy, PV sources can operate in the MPPT mode or adaptively switch to the power dispatch mode to flexibly regulate its output power to track the power reference. The characteristic curve fitting method does not require an irradiation sensor, but it has a more stable performance under rapid and continuous change in irradiation with simple calculation and error control since its extremely high similarity with the P–U characteristics of the PV source. Simulation is performed based on a detailed PV dynamic model to validate the proposed control strategy.