Study On Bed Temperature Control System Of Multivariable Circulating Fluidized Bed Boiler Based On Fractional Order PI~?D~? Controller

The bed temperature control system of circulating fluidized bed boiler is a thermal system with large lag,non-linearity,strong disturbance,time-varying and multi-variable coupling.It also carries out heat transfer,gas-solid two-phase flow,combustion and other processes.In addition,it is subject to a variety of disturbances,under a variety of disturbances,and also adapt to the situation of variable load,the bed temperature control system of circulating fluidized bed boiler has not been better handled well.In actual operation,it is mainly controlled by conventional PID control algorithm,and its rate of auto-controlr is low,disturbance rejection is poor and robustness is bad.Different from integer-order PID controller,fractional-order PI~?D~? controller adds two adjustable parameters?and? .It has more stable region and adjustable range than before.It has better control quality and robust performance for the thermal plant of circulating fluidized bed boiler with large delay and inertia.Up to now,there are few literatures on thermal control based on fractional calculus,and there are fewer fractional PI~?D~? controllers used in thermal systems such as circulating fluidized bed boilers.Therefore,this thesis introduces fractional PI~?D~? controller,which is applied to the bed temperature control of circulating fluidized bed boiler,and designs a controller with better control accuracy.In this thesis,main works are as follow:1.The types of fractional controllers,the tuning method and the current status of circulating fluidized bed boiler control are reviewed.Several important functions of fractional calculus theory are introduced in detail,and three different definitions of fractional order are described,a large number of examples are given.For a widely used 75t/h circulating fluidized bed boiler bed temperature system model,the model is analyzed and the effects of various variables on the bed temperature system are discussed in detail.2.A fractional-order PI~?D~? controller for a circulating fluidized bed boiler bed temperature system is proposed.The five parameters of the fractional-order PI~?D~? controller are subjected to variable analysis to understand its performance impact on the fractional-order PI~?D~? controller.On this basis,the current method for the fractional-order PI~?D~? controller tuning method mostly uses the phase margin method and the amplitude margin method to obtain the control parameters,this method is cumbersome and not suitable for engineering tuning.This thesis introduces several simple engineering setting methods,and applies this method to the circulating fluidized bed boiler bed temperature control system.The performance analysis and comparison are carried out,and a better engineering tuning method is obtained.3.A fractional PI~?D~? control strategy for multivariable bed temperature and main steam pressure of circulating fluidized bed boilers is proposed.In view of the fact that the bed temperature control of circulating fluidized bed boiler is still in the condition of single variable loop control,this thesis introduces the inverse decoupling method based on the analysis of previous methods,and designs a fractional PI~?D~? controller system for the multi-variable bed temperature and main steam pressure control of circulating fluidized bed boiler.4.An improved PSO algorithm is proposed to optimize the fractional PI~?D~? controller,and the optimal controller is applied to the multi-variable bed temperature and main steam pressure control system of circulating fluidized bed boilers.The advantages and disadvantages of the improved method are analyzed in detail,and some indexes are discussed in detail.The model adaptability,disturbance rejection,variable load and Monte Carlo experiments of the optimal controller are carried out.