Stability Identification and controllers self-tuning procedures applied to electronic power converter in microgrid

Abstract

The scenario defined by a microgrid with distributed-generation presents an intensive use of electronic power converters that are responsible for connecting power sources (in general DC) to the distribution network. In the situation in which the microgrid is connected to the external system, it is possible to import or export the energy produced or demanded inside the microgrid. The external source establishes the voltage on the bus. When the microgrid operates islanded, i.e. disconnected from the external network, one of the converters must assume the role of grid former, that is, it establishes the voltage that will serve as a reference for the operation of the other converters (which typically operate controlling the output current). The quality and stability of the voltage produced by such a converter plays an essential role for the operation of the entire microgrid. The stability of the control of a converter depends on the relationship between the output impedance of the converter and the input impedance of the remainder of the grid (anything connected to the network at the common coupling point). Such impedance "seen" by the converter changes continuously because it depends on the behavior of all other converters. This behavior can lead to problems of instability for the network former. This project proposes the development of an online system to identify the stability conditions of the grid-forming converter and, from the identification performed, automatically changing the controllers to get enough margin of stability. The converter is three-phase, four-wire and has on its DC side a battery bank so that it is able to supply and absorb active power. The project provides for modeling, simulations and experimental checks in LabRei microgrid, linked to FAPESP thematic project. (AU)