Design and Control of Microgrid Fed by Renewable Energy Generating Sources

This paper presents a control of a microgrid at an isolated location fed from wind and solar based hybrid energy sources. The machine used for wind energy conversion is doubly fed induction generator (DFIG) and a battery bank is connected to a common dc bus of them. A solar photovoltaic (PV) array is used to convert solar power, which is evacuated at the common dc bus of DFIG using a dc–dc boost converter in a cost effective way. The voltage and frequency are controlled through an indirect vector control of the line side converter, which is incorporated with droop characteristics. It alters the frequency set point based on the energy level of the battery, which slows down over charging or discharging of the battery. The system is also able to work when wind power source is unavailable. Both wind and solar energy blocks have maximum power point tracking (MPPT) in their control algorithm. The system is designed for complete automatic operation taking consideration of all the practical conditions. The system is also provided with a provision of external power support for the battery charging without any additional requirement. A simulation model of system is developed in MATLAB environment and simulation results are presented for various conditions, e.g., unavailability of wind or solar energies, unbalanced and nonlinear loads, and low state of charge of the battery. Finally, a prototype of the system is implemented using a 5-kW solar PV array simulator and a 3.7-kW wound rotor induction machine and experimental results are produced to reaffirm the theoretical model and design.