MMC Based Solid State Transformer for Large-Scale Distributed PV Integration and Medium Voltage AC/DC Interconnection

This paper proposes a novel multiport modular multilevel converter-based solid state transformer (MMC-SST) with a distributed control system architecture for large-scale PV integration and medium-voltage AC/DC interconnection. The distributed arrangement of PV arrays within the proposed topology enables the implementation of distributed maximum power point tracking (DMPPT), which mitigates the effects of partial shading and enhances energy harvesting from PV arrays. The symmetric design of the proposed MMC-SST eliminates the common power imbalance issue in MMC-based PV inverters. Additionally, the symmetric design of sub-MMC modules introduced in this paper makes it possible to suppress capacitor voltage ripples and differential currents effectively without the need for measuring arm currents. As a result, the proposed MMC-SST requires a smaller capacitor size, fewer current sensors, and lower isolated communications. Several case studies are conducted, and hardware-in-the-loop (HIL) simulation results are provided to validate the performance of the proposed MMC-SST and designed control system.