Study of a Low Voltage DC Micro Grid Based on a Solid-State Transformer Under Different Operating Conditions in Smart Grid Distribution

Abstract

This study focuses on developing a suitable control strategy to control a Low Voltage DC (LVDC) distribution system based on a three-stage Solid State Transformer (SST). It supplies AC loads using Distributed Generation (DG) from renewable photovoltaic (PV) energy sources. The proposed system is divided into two main architectures, namely, the SST and the LVDC microgrid (µG). For applications involving the smart grid, the SST is essential. Due to its numerous advantages and capabilities, it is a high potential replacement for the conventional transformer. For example, it enables real-time voltage regulation, two-way power control, and the syncing of renewable energy systems with the distribution grid. The three-stage topology is the most reliable and effective SST topology currently in use when connected to the smart grid.

The LVDC µG, constituted of 3 subsystems, is connected through the low voltage output of the SST which increases the efficiency of the overall system, improves power quality by regulating and stabilizing the LVDC µG voltage, and enables the integration of different renewable energies. A global supervisory strategy for the LVDC µG based on SST is also being developed based on a cooperative approach to coordinate the power flow between different components of a smart grid. This control strategy was proposed to ensure optimal operation and performance of the overall system and to enhance the quality of the low DC voltage on the SST side during oscillations in the µG output. The developed control strategy leads to maximizing the contribution of the PV energy to fulfill the load demand and, therefore, minimizing the reliance of the storage system to extend its lifetime and alleviate the pressure on the main grid.