Analysis and optimized control of dead-time effects in dual active bridge converters to eliminate voltage hazards under high switching frequency

Dual Active Bridge (DAB) converters are more commonly deployed in renewable energy systems, electric vehicles, advanced energy storage, and distributed power grids than conventional DC-DC converters due to the advantages of electrical isolation, high power density, and zero voltage switching (ZVS) capability. Existing studies on DAB mainly focus on conduction loss, reflux power loss, current stress, and high-frequency oscillation based on ideal states, which do not thoroughly consider the dead-time effect. As switching frequencies increase, dead-time causes severe operational hazards such as voltage polarity reversal and voltage sag, potentially damaging power devices. However, existing research addressing dead-time is limited to basic control strategies. To extensively exploit the performance potential of DAB converters, this paper proposes a current stress-optimized Variable Mode Extended-Phase-Shift (VM-EPS) control scheme that explicitly considers dead-time effects. By deriving exact operational characteristics across ten non-ideal modes, the proposed scheme coordinates specific operating modes for light, medium, and heavy load scenarios. By formulating and solving the current stress optimization problem using the Karush-Kuhn-Tucker (KKT) method, optimal phase-shift and dead-time ratios for each mode is designed and eliminates dead-time-induced voltage hazards across the approximate full power range. To summarize, the optimized control achieves approximate full-range ZVS, enabling true soft-switching operation. Experimental validation confirms the effectiveness of the proposed method in eliminating voltage hazards, optimizing current stress, and enhancing the overall performance of DAB converters.