This paper presents a detailed nonlinear study of a hybrid power source (HPS) and powertrain topology in fuel cell electric vehicles (FCEVs). Two type of HPSs are consisted and compared; 1) fuel cell (FC) as the main source, and ultracapacitor (UC) as the auxiliary sources, 2) FC as the main source, and battery and UC as the auxiliary sources. A DC/DC boost converter interfaces between FC and Dc-Link, and two buck-boost converters connect UC and battery to DC-Link respectively. Dynamic model of FCEVs with different HPS are developed based on the nonlinear behavior of subsystems. The main purpose is to design a controller for simultaneous control of DC/DC converters. This paper proposes a nonlinear control approach based on Lyapunov theory to insure following control objectives: 1- regulation of the DC -link voltage, 2- definition of FC reference current, 3- impeccable tracking of power sources' reference currents. The asymptotic stability of the closed loop systems are also insured in various conditions. The performance of the proposed controllers is validated and compared via numerical simulations. The simulation results show that the UC and battery can assist the FC to meet the load demand and improve its performance. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.