Novel sensorless generator control and grid fault ride-through strategies for variable-speed wind turbines and implementation on a new real-time simulation platform

This thesis contains studies regarding the modeling, control, and protection of variablespeed wind turbines and the real-time implementation. The usage of MW-size variable-speed wind turbines as sources of energy has increased significantly during the last decade. Advantages over fixed-speed wind turbines include more efficient wind power extraction, reduced grid power fluctuation, and improved grid reactive power support. Two types of typical generation systems for large-size variable-speed wind turbines exist. One is the doubly-fed induction generator (DFIG) with a partial-scale power electronic converter. The other is the permanent-magnet synchronous generator (PMSG) with a full-scale power electronic converter. This thesis is to address the modeling of these two wind turbine systems, including the complete aerodynamic and mechanical and electrical components. In this context, this thesis gives special focus on the mechanical sensorless control and grid fault ride-through strategies of variable-speed wind turbines. Improved solutions are analyzed and verified. In the electrical controller of a DFIG, A mechanical speed sensor is normally required to provide accurate information of the machine speed and rotor position. However, sensorless operation is desirable because the use of a mechanical speed sensor coupled with the machine shaft has several drawbacks in terms of degraded robustness, extra cost and cabling, and difficult maintenance. In this thesis, the design and analysis of a new sensorless vector controller using a reduced-order state observer is addressed in detail. Results have revealed that the proposed sensorless observer is more robust against parameter variations than other speed estimation schemes.