Power Electronic Transformer for Advanced Grid Management in Presence of Distributed Generation

摘要

Innovative architectures for electric energy distribution grids (e.g., microgrid, LoCal grid) have recently been proposed that virtualize a local generator as a constant load, source, or zero load to the grid, making it possible to connect distributed generation into the grid without reducing its reliability. Using these architectures, distributed generation may enhance the stability of the power grid. A new strategy is here proposed to improve the efficiency, flexibility, and stability of smart grids. This paper deals with a high performance solution based on a Power Electronic Transformer (PET), which includes dc-links, multilevel converters, and a medium-frequency (MF) transformer. Together with the reduced size of the whole conversion apparatus, the proposed topology ensures the compatibility of the distribution system and grid by appropriate strategy management. Good levels for the power quality indexes of the grid are obtained with a multilevel NPC front-end: mainly low values of harmonic distortion, and voltage and current dissymmetry. This occurs even if the commutation frequency of the switching devices of this converter is not high (1÷2 kHz). This paper mainly focuses on the control technique for the multilevel converters connected to the primary and secondary windings of the MF transformer, imposing multistep- or square-wave voltages. Control algorithms are presented that successfully meet the demands of the grid, and cases-studies are compared under ordinary and heavy conditions.