This paper presents a fuzzy based frequency control strategy by grid-connected MW class PV generation. The frequency control is proposed from the view point of the frequency fluctuation problem produced by the large penetration of PV power. The fuzzy control has three inputs: average insolation, change of insolation and system frequency deviation. Following these three inputs, a frequency control system of the PV inverters is proposed. For the case of different insolations, a coordinated inverter and battery control method is presented. The proposed method is simulated in three control area power system by considering dual power and information flows between supply and demand sides and is found satisfactory to provide frequency control and to reduce tie-line power fluctuations.