Estimate of Looking Back Impedance of Photovoltaic Power Generation Connected to Low-voltage Line

Abstract

The paper examines the looking back impedance of photovoltaic power generation (PV) connected to a low voltage line. Although the impedance is one of the vital factors in managing voltage profiles of a power system, few studies have been reported on the impedance. This paper proposes two estimation methods of the impedance using regression and spectral analyses techniques. Since a power factor for the PVs under study is assumed to be unity, the resistance component of the impedance is estimated with the methods. The methods are applied to the actual data obtained for 28 PVs. The estimated resistance with the two methods closely agrees with each other; this implicates the validity of the estimate. The estimates show that the looking back resistance exhibits more than one order difference among the PVs and tends to be smaller for a PV connected to a three phase three wire system than for that connected to a single phase three wire system. The seasonal variations of the resistance are also discussed in this paper.