I. Introduction
DUE to the depletion of fossil energy and environmental protection issues, renewable energy such as the wind and the solar energy have been widely used for a few decades [1]. Specially, the solar energy has the advantages of free, no pollution, low maintenance cost, distributed through the earth, and no noise due to the absence of the moving parts. Two principal types of PV power system exist, which are classified by their functions and configuration, namely: one is standalone system and the other is grid-connected system [2]–[5]. The operation of stand-alone PV systems is suitable for low power application. On the other hands, grid-connected system is mainly used for high power application independent of the electric utility grid.