Resumen de Intelligent connection agent for three-phase grid-connected microgrids
The high penetration of renewable energy systems is boosting the distributed power generation systems connected to the electrical network in microgrid structures. This concept permits to form local networks able to work out of the mains, when the grid is under fault conditions. One of the most important aspects of grid-connected inverters lies in synchronization with the grid phase. To detect the grid angle, the phase synchronization loops presents a good performance under balanced grids, but its behavior worsens under perturbations and harmonics.
With the use of advanced synchronization algorithms, based on the frequency, case, the removal of the positive sequence is facilitated, even in presence of harmonics, based on frequency detection systems. A robust model in front of grid faults working in ¿-ß frame has been implemented using proportional-resonant control loops, and especially the use of the DSOGI-FLL algorithm as a synchronization tool. This thesis presents a method to perform the intentional disconnection and reconnection process of local grids from the main distribution grid, when it is affected by a fault. The Intelligent Connection Agent (ICA), formed by a voltage source inverter (VSI) and a controlled switch, is grid synchronized (with a DSOGI-FLL) and controlled in stationary reference frame, in ¿-ß. The VSI control establishes the state of the switch, determining if the microgrid is connected to the grid or not. Therefore, VSI works as a grid observer or as a grid former, in function of presence of any fault in the mains. It will work like a grid-observer but, under any grid failure, the ICA disconnects the microgrid from the main grid and forms a nominal voltage reference for the power source inverters and loadsconnected into the microgrid.
The simulations and experimental results had shown a good performance and a fast dynamics of the proposed system so in disconnection and in reconnection transient.
