Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Electrical and Computer Engineering


Dr. Amirnaser Yazdani


This thesis is mainly focused on (i) mathematical modeling and real power control of a direct-drive wind energy conversion system (WECS) that employs a high-pole permanent-magnet synchronous generator (PMSG), and (ii) the contribution of the WECS to the frequency regulation process in a host power system. In the first part, a strategy is proposed for real power control of the WECS, which augments the maximum power-point tracking (MPPT) feature of modern WECSs. The proposed strategy is based on rapid torque control, rather than the (slow) pitch-angle control. Moreover, a supplementary damping scheme is presented and tuned for the proposed power control strategy, based on a detailed mathematical model and eigenvalue analysis of the WECS. The supplementary mechanism damps the WECS drive-train oscillations and maintains its internal stability, even if its output power is regulated. The thesis also presents an alternative control structure for the WECS which mitigates the sensitivity of the WECS output power to power fluctuations caused by wind speed variations and drive-train oscillatory modes. Thus, a damping strategy and a tuning procedure are proposed for the aforementioned control structure, such that a stable performance of the WECS over the operating range is ensured.

In the second part of the thesis, an enhanced control strategy is proposed that enables a WECS to contribute to frequency regulation process by effectively using its available generation reserve and the kinetic energy of its rotor, such that the stability of the WECS is maintained over the operating range. The performances of direct-drive PMSG-based WECSs with the proposed control strategy are examined in an example host power system and the impact of wind speed intermittency on the frequency responses of WECSs is assessed, based on which the parameters of the proposed control are adjusted to maintain the reliability of the example power system in response to a specific contingency event, under different wind speed regimes. The effectiveness of the proposed control strategies is demonstrated through time-domain simulation studies conducted in the PSCAD/EMTDC software environment.