Grid-connected PV-wind-fuel cell hybrid system employing a supercapacitor bank as storage device to supply a critical DC load

In this work a grid-connected renewable energy system composed by a lkW photovoltaic (PV) array and a 1 kW wind turbine (WT) is presented. The generated power from each renewable source is processed by independent dc-dc converters and provided to a common dc bus. Once batteries employment is not desired, a 1.2 kW fuel cell (FC) and a supercapacitor bank (SCB) are used as backup, in order to keep a dc critical load continuously supplied. The SCB operates as a short term storage device and its use also ensure the 120 Hz voltage ripple attenuation. From proper process, the dc bus power is delivered to the main grid with high power factor. This paper presents all theoretical analysis referring the proposed system, including the MPPT strategies for PV and WT generators and the control strategies for the system operation on grid-connected and stand alone modes. A complete power flow study is also presented, considering several combinations of power generation and load demand. Simulation results, obtained by the use of PSIM software, are accomplished in order to validate the system operation.