Operation and Hierarchical Coordination Control of Integrated Hybrid Distribution Transformer under Grid Fault Conditions

The hybrid distribution transformer (HDT) achieves a compromise between the low-frequency transformer (LFT) and the solid-state transformer (SST). It combines the LFT's efficiency and reliability with the added advantage of partial power controllability via an integrated converter. However, the existing research on the HDT fault ride-through does not consider the coordination relationship with its own safe operation constraints, while few studies have considered capacity coordination between multiple converters. Therefore, this paper proposes an improved hierarchical coordination control of integrated HDT (IHDT), considering grid fault and normal conditions. First, the IHDT topology is proposed, and the operation mechanism of IHDT to realize the voltage support and current compensation is clarified by analyzing the coupling mechanism between the converter and LFT. Furthermore, under complex conditions, the unified expressions of the IHDT winding voltage, current, and power are derived, the safe operation constraints of IHDT are analyzed, and a hierarchical coordination control strategy is proposed. Finally, the correctness and effectiveness of the IHDT topology and control strategy are demonstrated by simulation analysis and experimental verification.