A Modulation Method for Decoupling Capacitance Reduction in Single-Stage Dual-Active-Bridge Microinverters

Conventional single-stage dual active bridge (DAB) microinverters typically have a bulky capacitor for decoupling double-line frequency power and a significant pulsation in the input current, leading to reduced power density and degraded Maximum Power Point Tracking (MPPT) performance. This paper presents a new modulation method for single-stage DAB microinverters, allowing for substantial reductions in both the required decoupling capacitance and the input current ripple without hardware modifications. This is achieved by repurposing the inherent primary-side DC-blocking capacitor as an active decoupling capacitor. The operating principles of the proposed modulation scheme are comprehensively analyzed, and an automatic decoupling control system based on large-signal modelling is designed. A 500W experimental prototype is built for validation. Experimental results demonstrate that the proposed modulation method reduces the decoupling capacitor volume by 75% and decreases the double-line frequency pulsation in the input current by 96%, thereby improving the circuit's power density and MPPT accuracy.