The Research Of Control Methods For Variable-speed Constant-frequency Wind Energy Conversion System

In a variety of new energy, wind energy plays an important role in many developed countries. With the ongoing international cooperation, a variety of mature wind energy conversion (WECS) technology can gradually meet with various requirements.The main problem of wind power system is that wind energy is a random, filminic, unstable energy and the requirements of power quality are very strict. Therefore, without control technology, it is almost impossible to achieve the the performance of electricity market. In order to maximize the captured wind energy, connect wind turbine with grid and reduce the mechanical load, wind power generation technologies were paid much attention to. A series of key problems such as how to improve the reliability of the wind energy conversion system and maximize the captured wind energy have attracted more and more attention. And how to maximum the captured wind energy is the most important one, thus a lot of research work has been carried out by experts in the field of wind power.Using the frequency separation principle, Iulian Munteanu had established a two frequency loop model of WECS based on the Van der Hoven's spectral model of the wind speed. Motivated by the research results of Iulian Munteanu, in this paper, the model of the WECS was analyzed at first, and the maximum captured wind energy was taken as control objective below the rated wind speed, then the low and high frequency optimal controllers were designed based on the two frequency loop. In the low-frequency loop On-Off and PI controller were used, while in the high-frequency loop H∞state feedback and sliding-mode controllers were considered. In the end, simulation results indicatetramonate the effectiveness of the proposed control method.Because WECS are highly nonlinear systems, but with smooth nonlinearities, a possible optimal control design solution can be the feedback linearization control. Based on the strong nonlinearity of WECS, M.Chadli proposed to establish the dynamic model of WECS. Inspired by M.Chadli, the T-S fuzzy model of WECS is established in this paper. The model not only takes the nonlinearities of WECS into account, but also reduces the requirements of the original system. Although the dynamic characteristics of complex systems can be expressed by T-S fuzzy model, there will still be modeling errors. According to the typical nonlinear T-S fuzzy model, Zhang and other scholars propose to design a robust tracking controller. Based on this method, a fuzzy performance estimator is designed. Simulation results demonstrate that the T-S fuzzy model of WECS can accurately track the original system. With the proposed control method, the modeling error can be reduced, and it is feasible to maximize the wind energy capture ratio below rated wind speed.