Abstract
This paper describes the process of setting up an appropriate volt−var curve for the reactive power control of a photovoltaic (PV) inverter interconnected to a distribution line that is voltage controlled by a load ratio control transformer (LRT). Computer simulations with 360 patterns of volt−var curves applied to five actual distribution line models are presented. The number of patterns was narrowed down to 23 by using voltage, distribution-line loss, number of LRT tap operations, and a new evaluation index, the match ratio. When a power-factor constraint is imposed on the PV inverter, it may not output the reactive power according to the volt−var curve depending on the active power output. The match rate is an index to show the percentage of the operating points of the PV inverter that conform with the volt−var curve. By evaluating the match rate, it can be demonstrated if the PV inverter efficiently contributes to the voltage control, which greatly contributes to narrowing of the volt−var curve. It is demonstrated that the volt−var curve obtained using the proposed method is superior in terms of voltage controllability, distribution line losses, and the number of LRT tap controls.