Isolated MVdc-HVdc-AC Three-Port Power Router for High-Power Large-Scale PV Applications

This article proposes an isolated three-port power router (TP-PR) for medium-voltage (MV) dc collection of large-scale photovoltaic applications with a portion of ac power integration. By combining the modular multilevel converter (MMC) with thyristor valves through integrated transformers, not only the MVdc-side installed semiconductor capacity is reduced but also the requirement for MV-side submodule (SM) capacitor is eliminated. Particularly, the MMC utilizes high-frequency current for MV dc power transfer, effectively minimizing the requirement for SM capacitance. Moreover, the low on-state voltage drop of thyristors, along with zero-voltage switching and zero-current switching techniques, ensures low conversion loss for TP-PR. Compared with the traditional isolated three-port topology, TP-PR can reduce semiconductor cost by 22%, SM capacitance energy storage by 49%, and conversion loss by 50%. The operation principle, key parameters design, and multiport control strategy are introduced in detail. The effectiveness and the theoretical analysis have been confirmed by both simulation and experimental results.