Bi-level minimum loading unit commitment for small isolated power systems

The load demand of many non-interconnected island (NII) power systems exhibits high seasonal variability owing to the increased demand during the touristic summer season, against the low demand during the remaining year. The base load generating units of island systems are usually cheap, yet inflexible heavy fuel oil fired generators with large installed capacity and high technical minimum loading (TML) levels (in many cases up to 60% of the installed capacity). The higher TML of low-cost units renders them inflexible, particularly in low demand hours, where in some cases is necessary to dispatch flexible but costly peaking units (e.g. gas turbines), in order for the technical and security constraints of the unit commitment and economic dispatch (UC-ED) problem to be satisfied. This paper proposes a new UC ED method, solely based on the Mixed Integer Linear Programming (MILP) approach, incorporating a bi-level TML technique for the conventional units of isolated island power systems aiming at avoiding the commitment of costly generation during low demand days. The methodology is applied to two indicative study-case islands and the obtained results are analyzed and discussed.