Integrated Optimization Method Under Optimized Asymmetrical Duty Modulation Scheme for DAB-Based Energy Storage System With Comprehensive Soft-Switching Characteristics Analysis

With the increasing demand and fast advancement of distributed energy storage systems, dual-active-bridge (DAB) converter has become a popular interface circuit with a simple circuit structure, bidirectional power transmission ability, and simple control scheme. To improve efficiency performance of DAB converter, in this article, an optimized asymmetrical duty modulation scheme (OAS) is proposed to widen soft-switching region and reduce current level. On the one hand, operation principles, power characteristics, and current characteristics under different OAS modes are displayed systematically. For soft-switching characteristics modelings under proposed OAS, influences of both dead time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{d}$ </tex-math></inline-formula> and junction capacitance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C} _{\text {oss}}$ </tex-math></inline-formula> are taken into consideration. Electrical characteristics for resonant process within dead time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{d}$ </tex-math></inline-formula> are also modeled and analyzed. Meanwhile, based on the energy balance principle and the relationship between junction capacitance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C} _{\text {oss}}$ </tex-math></inline-formula> and drain-to-source voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {ds}}$ </tex-math></inline-formula>, the minimum current value to achieve zero voltage switching (ZVS) turn-on of switches can be obtained. On the other hand, to obtain better efficiency performance, an integrated optimization method is proposed. Based on the multiobjective particle swarm optimization (MOPSO) algorithm, root mean square (rms) current value, peak current, and soft-switching range can be optimized simultaneously. Through comprehensive comparisons with existing modulation schemes, the proposed OAS can achieve the lowest peak current, lowest rms current, and widest ZVS range. Finally, a DAB-based prototype is established and the effectiveness and correctness of the proposed method can be verified.