Multi-objective Optimal Control Of Permanent Magnet Synchronous Wind Turbine

With the rapid development of economy and society,the demand for energy is also growing rapidly.Overexploitation of fossil energy has led to the lack of reserves and environmental damage,which has become a major problem facing the progress of human society.The development of renewable energy is essential to alleviate energy shortage and protect the environment.In recent years,with the maturity of wind power generation technology,wind power generation has been developed and applied on a large scale.At present,the main control mode of wind turbine is to achieve maximum wind energy tracking control below rated wind speed and constant power control of generator above rated wind speed.Maximum wind energy tracking has always been the focus of attention.The PTD controller has the advantages of simple structure and easy realization.It is widely used in the design of system controller.However,due to the randomness of wind speed changes and the characteristics of wind turbine itself such as non-linearity and tim e-varying,it is innovative to overcome the shortcomings of traditional PID control to achieve maximum wind energy tracking in wind power non-linear control system.Because of the different control modes in the process of wind turbine control,it may cause severe vibration of tower and transmission chain,shorten the service life of wind turbine seriously,and even affect the safe operation of wind farm.Therefore,it is of great significance to synthesize the control mode of wind turbines with restraining the vibration of transmission chain,tower and reducing the fatigue load of wind turbines,so as to improve the generation capacity of wind turbines and ensure the safe operation of wind turbines.Firstly,the basic structure and working principle of permanent magnet synchronous wind turbine are introduced in detail,and the mathematical model of permanent magnet synchronous wind turbine is established.Aiming at the randomness of wind speed variation and the non-linearity and time-varying characteristics of wind turbine,a PID control strategy with model-free outer loop compensation is adopted to realize maximum wind energy tracking of wind turbine.This strategy adds an external loop based on model-free adaptive control to the traditional PID control system,and designs a model-free PID controller.By adjusting the three parameters of Kp,Ki and Kd,the error of tracking the optimal speed of wind turbine is close to zero,so that the maximum wind energy tracking control of wind turbine under rated wind speed can be realized.Secondly,in view of the problem that constant power control above rated wind speed may lead to severe vibration of transmission chain and thus affect the safe operation of the unit,two control objectives are proposed to suppress the fluctuation of output power of the generator and the fluctuation of transmission chain torque.Using LQR optimal control strategy,the state space expression of wind turbine is established,the optimal control law is determined by calculating the optimal gain matrix,and the LQR optimal controller is designed.By controlling the electromagnetic torque and pitch angle,the multi-objective optimal control of suppressing the fluctuation of generator output power and transmission chain torque above rated wind speed is finally realized.Based on the platform of MATLAB/SIMULINK,the proposed control strategy is simulated.The simulation results verify the effectiveness of the control strategy.