Research On Optimal Control Method Of Fractional Order PI~λD~μ Parameters For SCR Denitrification System

Thermal power generation has the advantages of large power generation,stable power output,flexible location selection,etc.,and occupies a dominant position in energy power generation in China.At present,the flue gas emission standard of thermal power plant is more and more strict,so it is urgent to study the safe,efficient and economical NO_x removal technology.Selective Catalytic Reduction（SCR）technology has been widely used in flue gas denitrification in thermal power plants due to its advantages of simple structure,reliable technology and high denitrification efficiency.Because the reaction mechanism of the SCR denitration system is complex and greatly affected by the operating conditions of the unit,it is difficult to accurately control the amount of ammonia injection by using traditional control methods.Therefore,this paper focuses on the in-depth study of the optimal control strategy of ammonia injection in SCR denitration system,aiming to reduce the NO_x concentration at the flue gas outlet and improve the control performance of the denitration system on the premise of ensuring the denitration efficiency and NH₃ escape standards.In order to analyze the main factors affecting the denitration efficiency of the system,this paper studies the process flow,layout and reaction principle of SCR denitration.Two conventional control methods of SCR denitrification system,fixed mole ratio control and fixed value control of NO_x outlet,are studied,and the SCR denitrification system under the above conventional control is simulated and analyzed.In order to solve the problems such as long adjustment time and large overshoot existing in conventional control methods of SCR denitration system,the basic theoretical knowledge of fractional calculus and the structure of fractional PI^λD^μcontroller are studied,the control performance of fractional-order PI^λD^μcontroller is analyzed,and the fractional PI^λD^μcontroller is introduced into SCR denitration control system.Due to the large number of parameters in the fractional-order PI^λD^μcontroller,the parameter optimization is difficult,and the traditional tuning method is time-consuming and easy to fall into the local optimum.Aiming at the shortcomings of traditional tuning methods,a parameter optimization algorithm with CMA-ES sampler Optuna is proposed.In this paper,the optimal performance of algorithm is validated with standard test functions,and through the example,the optimization algorithm in this paper is used to design a fractional-order PI^λD^μcontroller for a typical plant with delay,the experimental results show that with CMA-ES sampler Optuna optimization algorithm optimization ability,can effectively jump out of local extreme value point and the controller parameter setting precision,etc.According to the characteristics of the SCR denitration system and the problems existing in the traditional control scheme,the optimization algorithm in this paper is used to design the fractional-order PI^λD^μcontroller for the SCR denitration system.Smiulink is used to build an SCR denitration system model based on the CMA-ES sampler Optuna optimized fractional-order PI^λD^μcontrol,and three typical control schemes are selected for comparative experiments.The simulation results show that the SCR denitration system using the optimal control method in this paper has shorter rise time and adjustment time,smaller overshoot,faster and more stable system response in three aspects:set value tracking,anti-interference and robustness.The control scheme has high engineering application value.