The achievements and methods of linear optimal control used in the control of wind energy conversion system stability, speed control system and maximum-power transfer are surveyed, and certain problems to be solved are proposed simultaneously.

Based on analyzing the control strategy of maximal wind energy capture for variable speed constant frequency wind turbines,a control strategy was proposed by directly controlling the DFIG(doubly fed induction generator)rotor current to follow an optimal condition for not only the extracted maximum power of the wind turbine below the rated wind speed but also the copper loss minimization.

A controller for maximum wind energy capture of wind power system according to the theory of auto disturbance rejection controller has been presented.

A nonlinear feedback controller for maximum wind energy capture of wind energy conversion system (WECS) with passivity~based control (PBC) principle has been designed using pitch angle control of the blades and delay angle control of the rectifier.

Variable speed constant frequency wind power generation with doubly-fed inductor generation can obtain the maximal wind power tracking and utilize the wind energy to the maximum efficiency under rated wind speed.

So the study of how to control wind power generator to run at optimal rotor speed, namely maximal wind power tracking ,turn into available approach of enhancing variable speed constant frequency wind power generator operation efficiency.

Taking fish as example,this paper carries out a qualitative analysis of the model of the two species simultaneous harvesting,and then obtains the optimal harvesting policy by the optimal control theory.

It firstly discusses the quality of the equilibrium and proves the existence of the limit cycle,and then uses optimal control theory to obtain optimal harvesting strategy.

The optimal harvesting problem for a semi-linear age-dependent time-varying population system is discussed.