Closed-Loop Control of DC–DC Dual-Active-Bridge Converters Driving Single-Phase Inverters

TLDR

A solid‑state transformer is a high‑frequency power electronic device that typically consists of an ac‑dc rectifier, an isolated dc‑dc dual‑active‑bridge converter, and a dc‑ac inverter. This work develops a controller for the dc‑dc dual‑active‑bridge converter when it drives a regulated single‑phase dc‑ac inverter. The inverter is modeled as a 120‑Hz current sink, revealing that a PI controller has low gain at that frequency; two solutions are proposed—a band‑stop filter with feedforward and a proportional‑resonant controller in the feedback loop. Theoretical, simulation, and experimental results confirm the effectiveness of the proposed control strategies.

Abstract

A solid-state transformer (SST) is a high-frequency power electronic converter that is used as a distribution power transformer. A common three-stage configuration of an SST consists of ac-dc rectifier, isolated dc-dc dual-active-bridge (DAB) converter, and dc-ac inverter. This study addresses the controller design issue for a dc-dc DAB converter when driving a regulated single-phase dc-ac inverter. Since the switching frequency of the inverter stage is much higher than that of the DAB stage, the single-phase inverter is modeled as a double-line-frequency (e.g., 120 Hz) current sink. The effect of 120-Hz current by the single-phase inverter is studied. The limitation of a PI-controller, low gain at 120 Hz, is investigated. Two methods are proposed to improve the regulation of the output voltage of DAB converters. The first one uses a bandstop filter and feedforward, while the second method uses an additional proportional-resonant controller in the feedback loop. Theoretical analysis, simulation, and experiment results are provided.