Adaptive Virtual Bus Strategy for Electrolytic Capacitorless DAB Microinverters

In residential photovoltaic (PV) systems, microinverters link the PV panels to the ac bus. Conventionally, these microinverters incorporate a stable dc bus that relies on bulky and unreliable electrolytic capacitors. To improve, we propose an adaptive virtual bus strategy for DAB microinverter, which removes the electrolytic capacitors. The microinverter features a quasi-single-stage design interconnected by a virtual bus, which exhibits a notable double-line-frequency voltage ripple. The front-end employs a boost converter to elevate the low PV voltage and regulate the voltage of the virtual bus. The back-end utilizes a dual-active-bridge (DAB) inverter to transform the oscillating virtual bus voltage into the desired ac output. This architecture facilitates active power decoupling (APD) for enhanced power density by buffering mismatched power on the minimized bus capacitors and dynamically adjusting the operational state of the DAB inverter. Furthermore, by decoupling the control algorithms of the two parts, we reduce the number of required voltage and current sensors, thereby simplifying the overall control system. To validate the concept, a GaN-based prototype rated at 200 W and 600 kHz maximum is designed and tested. This prototype achieved a peak efficiency of 92.67%.