Modular Differential-Mode Solid-State Transformer

Solid-State Transformer (SST) technology is a promising alternative to conventional low-frequency transformers (LFTs), addressing key limitations in modern power systems. Traditionally, LFTs have been utilized for interconnecting regional grid networks, enabling efficient long-distance power transmission. However, their bulky and heavy monolithic structure poses challenges in transportation, replacement, and upgrading, which impedes the rapid modernization of grid infrastructure. In contrast, SST technology employs high frequency (HF) electric voltage is imposed across a transformer by leveraging power electronics to reduce the size of the overall system. This thesis presents a modular differential model (DM) SST technology based on single-stage differential mode ac/ac converter (DMAC). The proposed solution offers modular voltage and power scalability while ensuring high efficiency. A novel modulation scheme for the proposed DM-SST module allows high efficiency operation for wide operating range by ensuring zero voltage switching (ZVS) turn-on on all switches resulting in significant loss reduction in the converter. The current source nature of the input and output port of the DM-SST module greatly simplifies control for modular scaling, making the technology suitable for medium voltage systems. The DM-SST module is validated using a 1 kVA 220 V rated experimental prototype with peak efficiency of 97.6%. The proposed DM-SST is validated to offer wide output voltage regulation, reactive load handling capability, and reactive power compensation capability without the presence of DC-link capacitor, further enhancing the real-world application. The DM-SST system based on 3x2 module configuration is also implemented to demonstrate equal voltage balancing between the modules.