Identification of “Trouble Maker(s)” Caused by the PLL in Multi-paralleled Inverters Systems

In this paper, it is shown that in multi-paralleled inverters power systems, when the internal instability which is caused by an improperly designed phase-locked loop (PLL) takes place, the root mean square (RMS) value of the grid-injected current at the fundamental frequency of the “trouble maker(s)” will be lower than its reference value. The theoretical analysis is first carried out in details. Then, a diagnosis method is proposed to detect the exact “trouble maker(s)” and the PLL bandwidth of the “trouble maker(s)” can be adjusted online to continue injecting energy into the power grid. Finally, experimental results are presented, which verify the effectiveness of the proposed method.