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Islanding detection is a absolutely necessary function for Photovoltaic Grid-Connected Inverters and it is very important to detect the islanding accurately and quickly with less adverse impact on power quality. This paper proposes a positive feedback intermittent active frequency drift method which can decrease the adverse impact of frequency disturbance effectively within the time restrict of islanding detection according to that of traditional islanding detection methods. The theoretical analysis and simulation results show that this algorithm which is simple, effective, fast and have less adverse impact on power quality and has certain application value.

A MPPT (Maximum Power Point Tracking) control method of PV (Photovoltaic) generation system is proposed based on the shortcoming of the existing MPPT algorithms. The method applies CVT (Constant Voltage Tracking) algorithm to adjust the working point of PV array near the MPP (Maximum Power Point) for fast tracking when working point is far from MPP, and uses adapting duty cycle perturb method to optimize the steady state characteristic of MPP for effectively eliminate the output power oscillation under the setting precision. Its model is established and simulated with Matlab/Simulink.The CVT, duty cycle method and proposed methods are simulated respectively and simulation results show that, the proposed method tracks the MPP exactly and quickly and improves the energy conversion efficiency of PV generation system by eliminate the output power oscillation around MPP. Its fast response speed improves the static and dynamic performance of photovoltaic power system.