A High-Frequency-Link Single-Stage Three-Phase Cyclo-Active-Bridge Inverter

This paper presents the operating principles and hardware design of a grid-tied single-stage three-phase cyclo-active-bridge (CAB) inverter. Unlike traditional multistage inverters, the CAB inverter can directly interface a single dc source with a three-phase ac grid by merging a three-phase dual-active-bridge (DAB) with secondary-side cycloconverters. Each ac phase can be independently controlled by cyclo-phase-shift modulation, while maintaining high efficiency and a fast dynamic response. The single-stage design employs a high-frequency ac transformer link to bypass the need for large dc-link capacitors and filter inductors, while providing galvanic isolation and enabling bidirectional energy transfer. The dc side is handled by three half-bridge modules whose switched nodes are configured in a delta connection. On the ac side, three half-bridge cycloconverters provide independent ac outputs for their corresponding phases. Output power regulation of each phase is achieved via phase shifting between the primary side half-bridge and the secondary cycloconverter, facilitating decoupled power flow across phases for streamlined control and enhanced system flexibility. The Zero-Voltage-Switching (ZVS) operating conditions of both the primary side and the secondary side are analyzed. The planar magnetics design of high-frequency transformers and inductors is presented with core loss analysis through a wide operating range. A hardware prototype featuring a 48 V DC input, three-phase 240 Vrms ac outputs, and a total power rating of 600 W has been built and evaluated.