Adaptive Modulation of a CLC-Resonant DAB Converter for Wide Range ZVS Operation with Minimum Reactive Circulating Power

When compared to its non-resonant counterpart, the CLC-resonant dual active bridge (DAB) single-phase dc-dc converter can operate with reduced reactive power circulating between the two bridges. However, this DAB converter variant is known to have a limited zero voltage switching (ZVS) capability, particularly when operated at low power levels. This requires a trade-off between reducing switching losses by maintaining ZVS operation, and reducing conduction losses by minimizing the circulating reactive current. This paper investigates the CLC-resonant DAB converter's ZVS capability using analytical expressions that precisely predict the ZVS boundaries and presents analytical expressions for the active and reactive power in each bridge. Using this analysis, an adaptive modulation strategy is proposed that extends the ZVS operating regions while also maintaining the reactive circulating power at a minimum. The proposed modulation approach, converter ZVS capability, and reactive power reduction are validated through experiments on a single-phase CLC-resonant DAB.