The Research Of Multi-objective Optimal Control For Wind Energy Conversion System

Nowadays, energy and environment are the urgent problems that should be solved for human survival and development. It is provided with very important meanings to partially solve energy lack by using renewable energy source such as wind energy as the one of the most important clear substituted energy source in the future. Wind power generation has become the research focus of all countries along with the great development of the project of the wind power generation. A sery of key problems such as how to maximum the captured wind energy and improve the reliability of the wind energy conversion system (WECS) have attracted more and more attention. Therefore, the control technology for WECS has played the increasingly important role, as well as a large number of research achievements are obtained. Currently, much many literitures all take the maximum captured wind energy below the rated wind speed or the constant power output above the rated wind speed as a single control objective. However, the WECS is made of the wind turbine, drive train, generator, pitch blade servo system and AC-DC-AC converter, and it has more than one control objective. So the multi-objective control for WECS needs more intensive study. Some scholars has paid attention to it and given out some research achievements.According to the multi-time scale characteristic of the wind speed, Iulian Munteanu divides the wind speed into low-frequency component and high-frequency turbulent component by using the frequency separation principle. Below the rated wind speed, the maximum captured wind energy and decreasing the generator oscillation are taken as the control objectives, and the two-frequency-loop optimal controller is designed based on LQG control. Motivated by Iulian Munteanu, the two main results are obtained by using the two-frequency-loop control. The first one is that the constant power output of the generator and reducing the oscillation of the generator and the pitch blade are taked as the control objective above the rated wind speed, and the LQG two-frequency-loop optimal controller is designed. Simulation results destramonate the control method proposed is effective. The second one is that the multi-objective mixed H2/H∞control is introduced into the two-frequency-loop control in spite of the LQG controller, since LQG control strictly depends on the linearized model of the controlled system and the system parameters of WECS vary with the bad circumstance. The different minimum H2 indexes are solved by the regularity of the H∞indexes and the different trade-off can be obtained. At last, the simulation analysis is given out.