Adaptive reactive power control of PV power plants for improved power transfer capability under ultra-weak grid conditions

The Photovoltaic (PV) power plants are usually deployed in remote areas with the high solar irradiance, and their power transfer capabilities can be greatly limited by the large impedance of long-distance transmission lines. This paper investigates first the power transfer limit of the PV power plant with the Short-Circuit Ratio (SCR) close to 1. It explicitly identifies that a minimum SCR of 2 is required for the PV power plant to deliver the rated active power when operating with the unit power factor. Then, considering the reactive power compensation from PV inverters, the minimum SCR along with the different Power Factor (PF) is derived. An adaptive reactive power droop control is further proposed to improve the power Transfer capability of the PV power plant. Simulation results of a 20MW solar farm demonstrate that the proposed method can ensure the rated power transfer of PV power plant with SCR of 1.25, provided that PV inverters with PFmin=0.9 is used.