Offset Current Modulation Technique for Wide ZVS Range in Dual Active Bridge (DAB) DC-DC Converter

This article proposes a novel offset current modulation technique, which can add a new degree of freedom to the dual active bridge dc-dc converter. The concept of the proposed technique is to inject offset currents into the primary- and secondary-sides of the transformer. If the same offset currents are injected into both sides, dc bias does not occur in the magnetizing current of the transformer. Therefore, the offset current can be used as a new control variable without any adverse effects. When the proposed technique is applied to single phase shift (SPS) modulation, zero voltage switching (ZVS) characteristics can be further improved by realizing the ZVS of two more switches, leading to higher efficiency. Furthermore, the proposed control system can be configured with simple modification of the conventional control system. The optimal SPS modulation with the proposed technique is derived through theoretical loss optimization considering a tradeoff between conduction loss and switching loss. The feasibility of the proposed technique is verified using a 3.3 kW prototype with a 400 V input and 280-420 V output conditions.