Power quality analysis of a pilot microgrid supplied by a CHP system in Greece

The cooperation of Dispersed Generation (DG) units with storage devices to meet controllable loads constitutes a Microgrid. Microgrids are Low Voltages (LV) or in some cases Medium Voltages (MV) networks. The unique feature of Microgrids is that although they operate mostly interconnected to the upper level voltage distribution network, they can be automatically transferred to islanded mode, in case of faults in the upstream network. Microgrid structure is able to unlock the full potential of Distributed Energy Resources (DER) and allows the full exploitation of their advantages. The purpose of this paper is to study the power quality of the Combined Heat and Power (CHP) system installed in the frame of EU-DEEP project inside the premises of the National Technical University of Athens (NTUA). The Microgrid system also contains batteries with inverters and critical loads. The power quality is studied by taking into consideration voltage magnitude variations, frequency variations, voltage unbalance, voltage fluctuations, as well as light flicker and harmonic distortion. Furthermore, the transitions between the islanded operation mode and the connected one are studied. The measurements are compared with the limits given by power quality Standards, especially ΕΝ 50160. The power quality analysis came to the conclusion that the current harmonic distortion is the main disturbance, because a high current Total Harmonic Distortion (THD) factor was observed. In addition, it was observed that the flicker exceeds the Standards' limits in the islanded mode. At last, it should be noted that distributed power units like the one examined can improve continuity and support the main power supply in the event of a supply outage.