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The article focuses on control strategies of single-phase two-stage grid connected photovoltaic (PV) generation systems. The principle and digital implementation of instantaneous current control, based upon the parameters of the inverter, is presented. This method can be used to achieve accurate tracking results and lower Total Harmonic Distortion (THD) of current. A novel Phase Locked Loop (PLL) and P-Q decoupled current control for a single-phase inverter is adopted to stabilize DC voltage as well as facilitating islanding detection. The proposed islanding detection strategy takes frequency feedback as reactive current drift to deviate frequency on islanding condition. It has the advantage of continuous frequency shift without waveform deterioration. It is proved to be effective even under the worst-case islanding condition. The validity and effect of these control strategies is verified by computer simulations and experiment on the apparatus of PV generation systems.