In order to improve the modeling accuracy and limitation period of the large-scale photovoltaic power plant for electromechanical transient simulation

an online dynamic equivalent method for the large-scale photovoltaic plant is proposed. The inverter clustering indices are calculated online with the inverters clustered

while the equivalent scheme is generated based on clustering index threshold. The validity of the equivalent scheme is judged by comparing the power system transient response characteristics before and after equivalence and iterative modification is carried out. The proposed real-time working conditions based equivalent method is able to improve the accuracy of the model. To increase computational efficiency

the parameter sensitivities of inverters and transient response of the photovoltaic plant detailed model are calculated offline

and a data base is set up

for acquisition via online actual information matching. An example of real power grid has confirmed the validity of the method proposed. This work is supported by State Grid Corporation of China (No. SGCC-MPLG003-2012

No. 5442NY120025) and Jiangsu Provincial Natural Science Foundation of China (No. BK2011137).