A New Strategy for Capacitor Bank DC-Link voltage Control in Frequency Control of Renewable Stand-Alone Grid Considering Fuel-Cell Cold Start

This paper addresses the important task of voltage regulation of ultracapacitor (UC) in a hybrid wind turbine/photovoltaic (PV)/fuel cell (FC) autonomous microgrid. One of the problems with this type of grid is the fact that the load frequency regulation in an off-grid operating mode is not fast enough. Therefore, it is proposed to improve the control of the load frequency by using a UC bank. On the other hand, another problem is that the voltage of the UC decreases during the discharge due to compensating the power deficit, and the voltage of the capacitor must be in the authorized range. To address these issues, a new improved "droop" control is used for sharing electrical power between PV, FC, and UC banks, taking into account the UC voltage. In the proposed strategy, the presence of a capacitor has two advantages: increasing the frequency control speed, and saving excessive power. The main novelties of the proposed configuration are a) Cold start of the fuel cell is anticipated, b) Critical conditions of excessive power are considered and c) the improved droop control combined with the UC voltage control. Finally, a comparison of the proposed topology with similar counterparts from previous studies is made. To bring the simulation closer to reality, it uses a high-order mathematical model with nonlinear operating models of renewable energy systems and the real ultracapacitor model available on the market. The comparison demonstrates the satisfactory response of the proposed algorithm. The suggested method is applicable for rural and remote areas.

کلیدواژه ها:

frequency control ، Induction generator wind turbine (IGWT) ، Photovoltaic (PV) ، Solid oxide fuel cell (SOFC) ، Ultra-Capacitor (UC) ،