Research on a novel PLL based islanding detection technology for multi grid-connected inverters

Aiming at the problem that under the condition of multi grid-connection inverters, the dilution effect can easily cause islanding detection failure of Sandia Frequency Shift (SFS) method, a new phase locked loop based composite islanding detection strategy for multi grid-connected inverters is proposed. The proposed strategy combines Sandia Voltage Shift (SVS) and SFS islanding detection method to improve the success rate of multi grid-connection inverters islanding detection. In addition, the SVS method is put into use only when the condition is met, which can avoid its adverse effects on the system energy efficiency. Theoretical analysis and simulation results show that the proposed method can effectively detect the islanding in the presence of dilution effect.