Energy conversion and storage control for small wind turbine systems

Abstract

Nowadays, the wind power is one of the most promising renewable sources of energy. That is possible because of the fast development of the power electronics, variable speed drives and wind turbines. Wind energy conversion systems (WECS) are very studied because of their benefits and as a result a large variety of WECS are proposed in the literature. In this thesis a small-scale wind energy conversion system (SWECS) structure is proposed. All main components are described in detail and modeled. Also a speed estimator for the permanent magnet synchronous generator is elaborated. The proposed SWECS is simulated in a simplified way, to better explain and motivate the role of a supercapacitor, as storage element for transients. In order to study, test and implement SWECS and some control strategies for it, a direct torque control “hardware in the loop” wind turbine emulator is proposed, simulated, built, and tested. Due to wind’s unpredictable nature, maximum power point (MPP) control algorithm is the key component, necessary to extract the maximum available power from WECS. Two MPP controls are developed and validated by simulation and experimental results on the real time “hardware in the loop” wind turbine emulator. The first MPP strategy is based on wind turbine known characteristics, memorized in the control system. The second is a perturb and observe, maximum power point tracking fuzzy logic controller (MPPT-FLC) algorithm. Both strategies are tested under steps and real wind speed profile and are applied for two wind turbine types. A comparison between the two MPP controllers is presented, to highlight the most efficient energy conversion strategy. It is concluded that for all studied cases, MPPT–FLC is superior. Some results from the site, where a similar system was installed, are presented to prove that in real conditions the system works properly. Finally, the experimental setup details are presented as a part of the work. Each theoretical consideration is validated through simulations and experiments.