A Unified Design Approach of Optimal Transient Single-Phase-Shift Modulation for Nonresonant Dual-Active-Bridge Converter With Complete Transient DC-Offset Elimination

Abstract

The dynamics of nonresonant dual-active-bridge converter (DABC) are simultaneously affected by the transient modulation strategy and controller design. In general, inappropriate transient modulation strategies can lead to nonzero transient dc offsets in the inductor current and transformer’s magnetizing current, thus introducing excessive trajectory tracking error and time delays between the pulsewidth modulation generator and controller. Consequently, truly optimal transient responses cannot be achieved solely through a high-performance controller, unless the modulation-induced transient dc offsets can be completely eliminated. This article presents a comprehensive review of the optimized transient phase-shift modulation (OTPSM) strategies for single-phase-shift modulated DABC, and derives a novel optimal modulation method referred to as symmetric single-sided OTPSM (SS-OTPSM), which is based on a unified theoretical framework of OTPSM and an additional condition enabling a full elimination of all undesired transient dc offsets. The proposed SS-OTPSM can be easily and cost-effectively implemented in a cycle-by-cycle manner, and inherently compatible with fast controllers. Additionally, in order to more accurately match DABC’s power transfer model under SS-OTPSM, an enhanced model predictive controller (EMPC) is proposed. By a combined use of SS-OTPSM and EMPC, ultrafast and completely dc-offset-free dynamics can be achieved without measuring the inductor current. The effectiveness of the proposed schemes is verified by closed-loop simulation and experimental results.