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 variable-speed 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.;Nowadays, almost all the grid code specifications over the world have included fault ride-through requirements for grid-connected wind turbines. In US, as mandated by the Federal Energy Regulatory Commission (FERC) Order 661-A, wind farms are required to remain online in the presence of severe voltage disturbances as low as 0.0 pu, as measured at the high voltage side of the wind generator step-up transformer, for up to 9 cycles (150 ms). These strict requirements present a significant challenge to the existing wind turbine technologies. In this thesis, an improved technique combining the traditional crowbar protection circuit and the demagnetizing current to ride-through symmetrical grid voltage dips is analyzed and verified for a DFIG-based wind turbine. This method reduces the crowbar activation time and helps the wind turbine resume its normal operation as soon as the fault is less severe, even before the fault clearance. This thesis also proposes an improved fault ride-through technique for a PMSG-based wind turbine to mitigate the dc-link overvoltage. This technique can be directly embedded into the original wind turbine electrical controller without using any extra protection hardware. It ensures the dc-link voltage is kept within the acceptable range during a voltage dip and the post-disturbance recovery period.;In this thesis, a novel integrated simulation platform is developed based on industry standard simulation tools, RTDS(TM) and dSPACE(TM). The aforementioned wind generation systems and the proposed control and protection schemes are all modeled and implemented in real-time on this simulation platform. The necessary measures in hardware and software aspects to enable the collaborative simulation of these two industry standard simulators are addressed. Results have shown this integrated real-time simulation platform has broad application prospects in wind turbine control design and grid interconnection studies.