0093-9994 (c) 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2756031, IEEE Transactions on Industry Applications Abstract—A new zero voltage switching (ZVS) full-bridge DC- DC converter for battery charging is proposed in this paper. The proposed isolated DC-DC converter is used for the DC-DC conversion stage of electric vehicle charger. The primary switches in DC-DC converter turn-on at zero voltage over the battery charging range with the help of passive auxiliary circuit. The diode clamping circuit on the primary side minimizes the severity of voltage spikes across the secondary rectifier diodes which are commonly present in conventional full-bridge DC-DC converters. The main switches are controlled with asymmetrical pulse width modulation (APWM) technique resulting in higher efficiency. APWM reduces the current stress of the main switches and the circulating losses compared to the conventional phase-shift modulation (PSM) method by controlling the auxiliary inductor current over the entire operating range of the proposed converter. The steady-state analysis of auxiliary circuit and its design considerations are discussed in detail. A 100-kHz, 1.2-kW full- bridge DC-DC converter prototype is developed. The experimental results are presented to validate the analysis and efficiency of the proposed converter. Index Terms—Full-bridge DC-DC converter, battery charging, electric vehicle charger, voltage spikes, zero-voltage switching. I. INTRODUCTION Plug-in electric vehicles (EVs) are the promising solutions for nowadays transportation in view of reducing greenhouse gas emissions for livable and sustainable environment [1], [2]. The high voltage traction battery pack in EVs is typically charged from utility grid by an EV charger [3]. The general block diagram of two-stage on-board EV charger power conditioning system is shown in Fig. 1. The two-stage AC-DC and DC-DC power conversion system provides inherent low frequency ripple rejection in the output current. The front-end AC-DC power factor correction (PFC) stage converts the AC grid voltage to a regulated intermediate DC bus link voltage and also improves the quality of input current at the same time. The second stage DC-DC converter converts DC bus link voltage to a regulated DC output voltage to charge the battery pack providing electrical isolation between the grid supply and the traction battery. Full-bridge DC-DC converter topology [4], [5] is preferred for the second stage because of its high efficiency, high power density, high reliability, and isolation capability. However, the conventional full-bridge converter has the following disadvantages: loss of zero voltage switching (ZVS) during turn-on at light loads, secondary duty cycle loss, high circulating current and high voltage spikes on output rectifier diodes due to the leakage inductance of the transformer and the external series inductance. Full-load range ZVS can be achieved by adding auxiliary current source network to the conventional full-bridge DC-DC converter. A single inductor auxiliary current source network proposed in [6], [7] improves the ZVS range. However, the uncontrolled auxiliary current increases the circulating and conduction losses of the converter. The passive adaptive auxiliary current source networks are proposed in [8]-[16] where the auxiliary reactive current is adaptive with phase-shift between two legs of full- bridge DC-DC converter. In this approach, the peak value of auxiliary inductor current is minimum at large phase-shift (higher duty cycle) and progressively increased when the phase-shift is reduced. In battery charging applications, the converter is required to operate at higher duty cycle for the desired output voltage during light-loads in constant voltage (CV) charging mode. Therefore, the adaptive auxiliary circuit assisted topologies result in increased auxiliary current which increases circulating and auxiliary circuit losses during constant current (CC) charging mode when operated with phase-shift modulation (PSM). To further minimize these circulating losses, the auxiliary circuit current is controlled with active auxiliary circuits in [17]-[19] which increase the cost and complexity of the converter. Another major problem of the conventional full-bridge converters is the voltage spikes across secondary rectifier diodes due to the ringing between junction capacitance of rectifier diodes with the transformer leakage inductance. The voltage spikes are intensified with the increase in the leakage inductance of the power transformer and in the operating switching frequency of the converter. Therefore, the output rectifier diodes and the output filter have to be overrated to withstand voltage spikes. Overrated diodes lead to increased losses due to higher forward voltage drop and poor reverse recovery characteristics. Additionally, the voltage spikes significantly increase the electromagnetic interference (EMI) and reduce the reliability of the converter. Resistor-Capacitor- Diode (RCD) snubber circuits proposed in [20], [21] suppress the voltage spikes. The disadvantage of RCD snubber circuit is that the energy stored in the capacitor is dissipated in snubber resistor which considerably reduces the efficiency of the converter. Active clamp snubber circuit proposed in [22] A New ZVS Full-Bridge DC-DC Converter for Battery Charging with Reduced Losses over Full-Load Range Venkata Ravi Kishore Kanamarlapudi, Student Member, IEEE, Benfei Wang, Nandha Kumar Kandasamy, Member, IEEE, and Ping Lam So, Senior Member, IEEE Fig. 1. Block diagram of on-board EV charger power conditioning system.