Power Conditioning System for Microgrid Operation

  PGS E.ON ERC RWTH Aachen The structure of a microgrid

Microgrids (MGs) are emerging as a new paradigm to incorporate distributed energy resources (DER). However many DER units are connected through power electronics. In this case the microgrids’ dynamics will be substantially different from a normal grid, especially when the MG operates isolated. One of the main challenges in these kinds of scenarios is to ensure stability. Frequency control using converter-coupled distributed generation is the main research objective.

The need of reducing pollutant emissions require technological alternatives that can meet electrical energy demand while enabling greater use of ecological resources. One of these alternatives is the use of small-scale generation technologies connected to the distribution network as close as possible to the consumption sites. This alternative is called distributed generation (DG) and promotes the deployment of renewable energy sources.

One of the main features of DG is the use in smart grids to ride through failures by grid isolation. This feature can significantly improve the reliability of power systems.

In this context microgrids are defined as a set of loads and DG which can operate connected to the main grid or isolated as appropriate. During connected mode, the MG may be completely or partially supplied by the main grid or may inject power into it. During isolated mode, the MG operates as a small grid in which DG units are responsible for keeping the voltage and frequency within permissible limits.

Some solutions were already proposed, however, the MG’s dynamics have a major impact on the control design, which has not been addressed so far. Specifically the impact of MG’s dynamics on the different elements, like protection systems, is of major concern. The rapid variations in power demand or generation can cause relay tripping. The disconnection of generation or load due to rapid changes in frequency may be critical for isolated MGs due to bounded conditions. Therefore, during MG isolated operation it is not only important to set and keep the frequency but also to control the dynamic behavior.

This research proposes the design of control strategies able to set the frequency reference in isolated MG even in the absence of synchronous generation with the aim of improving the MG dynamics.