This thesis is concerned with the analysis of a variable duty cycle wireless battery charger in different operating modes. In recent years, traditional power transfer systems based on cable connections have been lost their popularity because of their lack of persistent access and mobility. In addition in some applications like electric vehicles, because of their high power and voltage levels, the safety considerations will be also important in using and recharging them. To overcome these problems of the battery-based systems, many efforts have been made to improve and ease their charging process and make it more simple and smart. As an elegant choice, the use of wireless power transfer technologies will be a safe and secure method for charging the battery-based systems. In fact, the use of this technology in various applications including electrical traortation systems has been largely increased. Inductive power transmission as one of the most efficient wireless power transmission technologies (especially at short distances) has attracted much attention and has been introduced as an optimal option for use in electric vehicle charging systems. In this thesis, after introducing a brief overview of various wireless power transmission technologies, the bases of inductive power transmission are explained. A proper topology for the application of this technology in the wireless charging system of electric vehicles is introduced. It is explained that how by proper control of converter duty-cycle, the system can attain different operating modes. The basic parameters of the system are introduced and the chosen topology analysed by the means of two different methods including the first harmonic approximation and time domain analysis. In both methods, the operation of the system is divided into two sections of continuous current (CCM) and discontinuous current (DCM) and then six different modes of CCM operation are introduced. In addition, the system equations are derived in both methods, and in the time domain analysis, it is possible to accurately determine any system variable at the desired time. Since the determination of the system's operating point plays a significant role in its optimal performance and stability, further detailed relations are developed to determine the boundary of the proposed modes in both the first harmonic approximation and the time domain study. Because of the high accuracy and reducing the simplistic assumptions in the time domain survey, consideration of the relationships and boundaries introduced in this study can lead to improved design and also the optimal control of the induction charging system. In the final section, through the simulation of the system in the PSIM software, as well as the implementation of an experimental setup, the theoretical results are evaluated and then, by comparing the basic parameters in each of the study methods with the results of the simulation and the practical results, the high accuracy and performance of the proposed time domain method are confirmed. Keywords : Wireless charging of electric vehicle, inductive power transfer, first harmonic approximation, time domain analysi