The use of Active Fiber Composite (AFC) instead of traditional ceramic piezoelectric materials is characterized by high flexibility and large displacements. However, energy-harvesting capabilities of AFC are relatively low. To remedy this drawback, it is necessary to optimize its geometry in order to increase the produced electrical power. An analytically model of the system including the structural, the piezoelectric as well as electromechanical coupling of AFC piezocomposite, is proposed. The model takes into account the use of interdigitated electrode (IDE) disposition. Large deflection of the flexible beam is taking into account using a nonlinear von-Karman strain. The piezoelectric cantilever beam is bi-layered in which a substrate layer is partially covered by an AFC piezocomposite patch. The model provides an improved approach to design and analyze the electrical performance of the considered energy harvester. It takes into account the quadratic distribution voltage between two constitutive IDE. The extended Hamilton principle and the Gauss law are used to derive a reduced-order model of the active fiber composite energy harvester using a Galerkin procedure. The limit-cycle solutions are calculated using a Finite-Difference Method (FDM). The obtained frequency-response curves of the harvested electrical voltage measured across the external resistor R representing the external load are validated using Finite Element model developed using ANSYS with a homogenized piezoelectric material.