Electric vehicles (EVs) are promising alternatives to fossil fuel based vehicles due to their eco-friendly nature. However, the major drawbacks with EVs are - high charging times of the battery and the battery range. Hence, proper battery charging is of utmost importance because it significantly affects the life of the battery and this in turn causes a reduction in the EV battery range. On-board chargers for EVs usually come with two-stage power conversion systems, where the first stage comprises an AC-DC converter with input power factor correction (PFC) and the second stage has a DC-DC converter in order to charge the battery at an appropriate voltage level. Dual Active Bridge (DAB) converter is one of the promising candidates for the DC-DC conversion stage because of its inherent soft switching capability without demanding any extra passive components, its bidirectional power transfer capabilities, higher power density, etc. This DAB converter experiences loss of zero voltage switching (ZVS) under non-unity voltage gains (as in battery loads) and at light load conditions. Losing ZVS being critical incurs significant switch turn-on power losses leading to a significant reduction in the battery charger's power efficiency.

This seminar talk presents a new ZVS detection technique for DAB converter and its implementation. It also presents a new ZVS range enhancement method for DAB converter using series connected switched inductors. The first part covers a simple ZVS detection method for the DAB converter where the voltage information of the switching device is monitored at the start of the turn-on transient in order to detect ZVS. This ZVS detection signal could be used to enhance the ZVS range of the DAB converter by making modulation or hardware-based modifications. Taking this further the second part of the talk covers a hardware-based method to enhance the ZVS range by varying the equivalent inductance of the DAB converter using a series connected inductor. The incoming inductor is optimally switched into the circuit at zero current crossing to avoid any voltage spikes. Finally. Suitable simulation and experimental results related to the ZVS detection technique and also the ZVS enhancement method for the DAB tested on an indigenously developed laboratory prototype consisting of a 2 kW DAB converter for EV charging application will be presented.