Dynamic Phasor-based Small-Signal Stability Analysis and Control of Solid State Transformer

The inability of the conventional grid to meet peak demand, maintain quality, continuity, and reliability in power supply is driving the growth of microgrids. However, creating a microgrid is more expensive because one of the key components, transformer, plays important role in the distribution network. The solid state transformer (SST) proposed by FREEDM centre is one of the most suitable alternatives for the conventional transformers which can help the business industries to justify the trade-off between investment and resilience. Acknowledging the importance of SST in future microgrids, this paper proposes a dynamic phasor (DP) based model for stability analysis of SST, allowing a tremendous simplification of analysis resulting in faster simulation, revealing dynamical coupling between various quantities, which is essential to modern power grids for real-time control in grid operation, especially during disturbances. Using the DP based model of SST which is further linearized, the main contribution of the paper is in proposing a modular and a cascade model of SST, the consequences of which are discussed from the point of view of ease of control and complexity. Also the challenges in integrating many SSTs with the grid are discussed.