A Variable-Frequency Phase-Shift Modulation Strategy for Single-Stage DAB Microinverter Considering Switch-Parallel Capacitances

To address the soft-switching failure issue in single-stage dual active bridge-based microinverters caused by switch-parallel capacitance, this article proposes a variable-frequency phase-shift modulation strategy. By constructing a full-time-domain model incorporating dead time, the global soft-switching boundaries considering switch-parallel capacitance are derived. Based on these boundaries, a variable-frequency phase-shift modulation strategy is developed with the objectives of minimizing circulating power and the rms current. Furthermore, practical operating constraints are taken into account, and the switching frequency and phase-shift angles are further optimized. Compared with conventional methods, the proposed strategy effectively resolves soft-switching failures caused by improper energy control of the switch-parallel capacitance, significantly improving soft-switching performance and circulating power suppression under fixed dead-time conditions. Finally, the effectiveness of the proposed control strategy is experimentally verified using a 600 W prototype.