Stability Assessment of Voltage Control Strategies for Smart Transformer-Fed Distribution Grid

The smart transformer (ST), a solid-state-based transformer with control and communication functionalities, determines the voltage of the low voltage (LV) network. Due to the similar control purpose, the classic multiple feedback loop (multiloop) voltage control strategies widely utilized in the uninterruptible power supply (UPS) application, can be considered for the control of ST LV converter. However, a fundamental difference between ST and UPS is the presence in LV grid of distributed generation integrated through power electronics interfaces and the dimension of the supplied grid. Emerging issues like stability and harmonic oscillations challenge the safe operation of the ST-fed grid. In order to explore the problems associated with the grid-converter-based devices, the impacts of the grid converters on various multiloop voltage control strategies have been studied in this paper. Optimal multiloop strategy has been found to offer stable operation to a ST-fed distribution grid under various conditions. Case studies in a CIGRÉ benchmark grid and experimental results are provided to verify the correctness of the theoretical analyses.