Abstract
This study mainly investigates the current and speed control strategies of a doubly-fed induction generator (DFIG), which is applied to a tidal stream turbine (TST). Indeed, DFIG using integer-order PI (IOPI) controller has been widely proposed in the applications with a similar system, especially in wind energy conversion system (WECS). However, these conventional controllers cannot deal with the problems caused by the parameter variations satisfactorily under complex and harsh operation conditions, and may even deteriorate the performance. As a result, a fractional-order PI (FOPI) controller is considered to improve the efficiency and performance of DFIG-based TST in this paper. The FOPI controller, developed from the traditional IOPI controller and the fractional calculus theory, has a lot of prominent merits in many aspects, such as robustness, stability, and dynamic performance. In this paper, the proposed control strategies are embedded into the whole TST model which contains the tidal stream turbine, and the generator. The obtained simulation results demonstrate the prominent effectiveness and advantages of the proposed strategies compared with the conventional IOPI controller in terms of overshoot, static error, adjustment time, and robustness. It implies that FOPI controller could be a good candidate in TST applications.
Highlights
Due to serious environmental problems caused by fossil fuels, renewable energy has become more and more attractive in recent years
doubly-fed induction generator (DFIG), which is always used in wind energy conversion system (WECS), is considered as a good candidate for tidal stream turbine (TST) [3]
For DFIG-based TST, the controller of the machine side mainly aims to extract the maximum energy from marine current flow
Summary
Due to serious environmental problems caused by fossil fuels, renewable energy has become more and more attractive in recent years. Many researchers have adopted the IOPI controller for TST with different generators in their studies [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] These papers mainly focused on the control strategies regarding the swell effect, flux-weakening strategy, power smoothing strategy, MPPT strategy, loss minimization strategy, dispatching and frequency strategies, etc.; and do not pay great attention to the robustness and dynamic performance of the system. FOPI controller is applied for both current and speed loops of DFIG-based TST; the robustness of the internal and external disturbances will be analyzed; the performance will be compared systematically with that of IOPI controller; the overall system performance will be evaluated. The performance of DFIG-based TST using IOPI and FOPI controllers is realized, analyzed, and compared
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