This paper proposes two modulation schemes for Dual Active Bridge (DAB) converters, with the aim of maximizing Zero Voltage Switching (ZVS) operation over a wide operational range. The first is a ZVS-optimized constant frequency modulation scheme, constructed based on the boundary conditions of ZVS operation. This scheme maximizes the number of ZVS events across a broad operational range and is easy to implement. Additionally, a variable frequency modulation scheme is proposed, enabling continuous full ZVS operation for the DAB converter at full power and eliminating the loss of ZVS due to transitioning between modulation regions. This functionality extends the full ZVS range, yielding improved Electromagnetic Interference (EMI) performance and overall power efficiency. The synergy of the proposed modulation schemes is particularly well-suited for applications like off-board Electric Vehicle (EV) charging. Experimental validation, conducted on an 11-kW DAB converter prototype with an output voltage range of 250V to 950V, demonstrates the efficacy of the proposed schemes in achieving ZVS and boosting converter efficiency.

A variable switching frequency modulation for the Dual Active Bridge (DAB) converter is proposed in this paper. With this variable switching frequency modulation, the DAB converter can be operated in the ZVS-beneficial operational modes without the necessity to transition to others, thus a larger ZVS range for the DAB converter can be achieved. This modulation has potential of providing higher power efficiency and better EMI performance for the DAB converter in wide voltage range applications such as Electric Vehicle (EV) charging. A DAB converter with the variable frequency modulation method is simulated, and its effectiveness on the ZVS performance is demonstrated.