Distributed Generation Systems Based on Hybrid Wind/Photovoltaic/Fuel Cell Structures

The distributed generation (DG) today attracts a large interest due to an even increasing demand of energy and the growth of awareness about the impact of conventional energy sources on the environment. Photovoltaic (PV) and wind power are two of the most promising renewable energy technologies. Fuel cell (FC) systems also show enormous potential in future DG applications, due to a fast technology development, high efficiency, environment friendliness and modularity. Hybrid systems encompassing wind, photovoltaic and FC generators are today revised as a viable solution to overcome the inner unreliability of renewable energy sources. The modelling and control of a hybrid wind/PV/FC DG system is addressed in this dissertation. Dynamic models for the main system components, namely: wind and PV energy generators, fuel cell, electrolyser, power electronic interfaces, battery, hydrogen storage tank, gas compressor, are developed and verified by experimental tests and simulation studies. Five different architectures of stand-alone hybrid power systems are considered, exploiting connections through DC and AC buses. Each configuration is managed through a specific control methodology. Based on suitable dynamic models, the five proposed stand-alone hybrid energy system configurations have been simulated using the MATLAB/Simulink/SimPowSysTM software environment. A comparison among those configurations has been performed on the basis of purposely developed performance indexes. According to obtained results the high voltage DC bus (HVDC) configuration reaches the best score among the five configurations. A Fuzzy logic based management of a stand-alone hybrid generator based on high voltage DC bus configuration has been developed to dynamically optimize the power flows among the different energy sources. The performances of the proposed strategy are evaluated by simulation in different operating conditions. The results confirm the effectiveness of the proposed strategy. A further goal of the thesis has been the development of a probabilistic approach to size step-up transformers for grid-connected wind farms. This approach is mainly based on the evaluation of the Loss of Produced Power Probability index (LPPP); the costs of the wind farm equipments are also taken into consideration.