Power Quality Improvement by Supercapacitor Energy Storage

Harnessing green and renewable sources of energy is a future solution that addresses rising energy demands and growing environmental concerns. Among these, tapping wind energy using wind turbines appears to be one of the most promising solutions. A wind energy conversion system captures kinetic energy of wind and converts it into electrical energy. By nature, availability of wind energy is stochastic and intermittent. In contrast, electric power system expects a steady and planned supply of energy. This thesis addresses the gap in characteristics of wind energy supply and conventional electric energy demand. This thesis considers a doubly fed induction generator (DFIG) connected to a wind turbine to harness wind energy. The proposed topology connects a Supercapacitor through a buck-boost chopper to the DC link of rotor circuit. The Supercapacitor works to perform the job of a flywheel. The thesis proposes an appropriate control system that controls the output of the DFIG to constant value (Pref) eliminating short-term fluctuations. This control system works to control the buck-boost chopper and works as a inner control loop. Thereafter, this thesis proposes and optimization algorithm that considers short-term forecasted wind speeds (energy) for several minutes. It then optimizes to determine a minimum set of output values of the DFIG (Pref). It ensures that output of the DFIG has minimum changes thus minimizing intermittency in the DFIG output. This optimization algorithm forms the outer loop in the overall control strategy. The complete system is implemented in Matlab/Simulink and analysed in this thesis. The results demonstrate that the inner and outer control loops work to minimize output power oscillations and improve power quality.