A Power Management in an Isolated Micro Grid withReduce Voltage Deviation of Ultra-Capacitor

This paper deals with the important task of voltagecontrol of the ultra-capacitor (UC) in an isolated grid-off windturbine (WT), photovoltaic (PV) and fuel cell (FC) islanding.Renewable and distributed energy resources have recently beenintroduced as alternative energy source due to pollution-freeoperation and no fossil fuel consumption. Among variousalternative sources, PV, WT, and FC are more desirable than theothers. The frequency control of an isolated network is not exactas enough. Therefore, to improve the frequency control, using anUC bank is proposed. In this paper improved droop control isutilized for the electric power sharing between PV, FC, and UC.The output power of WT is controlled based on wind speed tocapture the maximum energy from wind. If the frequency of gridis going to decrease, then the UC will boost the active powerrapidly, to keep the power balance. Meanwhile, the PV, WT, andfinally FC will increase the power generation, if possible, topreserve the UC charge. If the load demand is decreasing andextra energy source from wind, day-light, and hydrogen flue isavailable, then the electric power sources supply the load andgenerate exceed power to charge the UC. Supposing that the loadis very light and the FC produces minimum power and the UC isfully charged. In this case, if WT and/or PV continue maximumpower extraction then the UC starts to over change and an overvoltagewill occur on the dc terminal voltage of the UC whichmay damage the insulation (di-electric) of the capacitor units.Therefore, a voltage control on UC terminal is unavoidable.

Keywords:

Frequency Control , Wind Turbine (IGWT) , SolidOxide Fuel cell (SOFC) , Ultra-Capacitor (UC) , Photovoltaic (PV) , Isolated Network , Fuzzy Controller