Grid-Integration of Wind Energy Systems: Control Design, Stability and Power Quality Issues

this chapter presents a comprehensive coverage on the modeling and control design of variable speed wind energy conversion systems. Different wind turbine, generator configurations and converter topologies are presented. The stability and power quality issues are also studied. In the simulation studies presented a squirrel-cage induction generator (SCIG)-based wind energy conversion system (WECS) is considered. The first control scheme considered in this chapter is based on vector control theory. Indirect field oriented control (IFOC) scheme with proportional and integral (PI) are designed for SCIG speed control. A simple maximum power point tracking (MPPT) strategy is used to determine the optimal speed under variable wind speed conditions which is then used as the reference in the IFOC scheme. Power flow between the supply and the inverter is regulated via simultaneous control of the active and reactive currents of the grid and the DC link voltage.
The second control approach discussed in this chapter is based on direct torque control (DTC) theory which has been successfully used to a variety of high performance industrial AC drives. The DTC space vector modulation (DTC-SVM) is designed and applied to two and three level voltage source inverter (VSI) to improve the energy efficiency of the variable speed SCIG-based WECS. Three different topologies are proposed to control the torque and flux of the SCIG. A series of simulations are presented to demonstrate the performance of these proposed control schemes under a variety of operating conditions including symmetrical and asymmetrical faults. Electric power quality issues are also analysed and discussed in terms of harmonics and compared with respect to different converter topologies and control strategies.