Research Of Nonlinear Control For Marine Supercharged Boiler Combustion System

Supercharged boiler is the main equipment of marine steam power plant,which provides power,electric power and heat energy for ship operation and daily life.Supercharged boiler dynamic performance directly influences the safe and stable operation of marine steam power.and development of supercharged boiler control system research has important theoretical and practical value.Variable conditions air/fuel optimization matching control has been the problem of supercharged boiler control,also is the main factor that affects the working stability,economy and emission performance of steam power device.The traditional control system usually adopts PID control strategy,which can not achieve the fast track of air flow to the fuel flow under variable conditions,and ensure that the air/fuel ratio is always controlled in an ideal range,resulting in deterioration of combustion state.Stable control of main steam pressure is the fundamental guarantee of stable,reliable operation for the steam turbine.Main steam pressure control system is a typical nonlinear,delay,multi-parameter and strong coupling system.Through simplifying the main steam pressure control system to linear,single variable system.and ignoring the coupling effect between the parameters,the developed control system is unable to meet the rapid and stability requirements of main steam pressure under variable loads,therefore the following research work is done in this thesis:1)Considering the influence of pressurized combustion to furnace volume heat load,furnace convective heat exchange,which were integrated into energy conservation,and adopting KB76 thermodynamic calculation to calculate the furnace flue gas temperature,solved the problem of low model calculation accuracy caused by neglecting pressurized combustion and furnace convective heat transfer.Aimed at the problem that the compressor,gas turbine and assistant steam turbine of turbocharged are driven by different refrigerants,modify the turbine gas group of graphics library to adapt modeling requirement respectively.In order to solve the problem that turbine have different operating characteristics under different working conditions,embed and interpolate the experimental running curve into simulation model calculation,to approximate operation characteristics of real turbocharger unit,and improve the model accuracy.2)Turbocharged mainly responded for providing required pressurized air in the whole operating range for high,stable and reliable work of boiler,which is driven by the flue gas turbine and auxiliary steam turbine.Turbocharged set has large inertia and time lag relative to boiler under conditions change,and when flue gas energy is not enough to push the turbocharged in part load and high load,to generate enough pressurized air to meet the reasonable needs of the air/fuel ratio,turbocharged must rely on the assistant turbine to provide the necessary impetus to drive,thus,the control difficulty lies in the coordinated control of supercharged boiler,gas turbine and assistant steam turbine.For the hybrid behavior characteristics with continuous dynamics and discrete event interacting that demonstrated by turbocharged set in operation process,presente the control method based on cooperation constraint arc Petri net,and establish the control model of turbocharged set based on hierarchical structure cooperation constraint arc Petri net,to solve the poor air/fuel ratio problem caused by air flow lag.3)Main steam pressure of supercharged boiler is mainly affected by the fuel flow and main steam flow,which is represented by that there is large time lag from fuel combustion to main steam pressure response with the characteristic of strong nonlinear.and effect of main steam flow to main steam pressure is fast,thus,the control difficulty is to regulate fuel flow quickly to compensate the change caused by main steam fluctuation,to maintain the main steam pressure in the reasonable range.Aimed at the problem of low predictive accuracy caused by using fuel flow alone to predictive main steam pressure,which affect the control performance,extend the Hammerstein model to two inputs Hammerstein model,and integrate fuel flow and main steam flow into input variables,to establish the normalized two inputs Hammerstein model,which solved the problem that system nonlinear,multivariable coupled and time-varying characteristics under variable conditions reduce the identification accuracy.To further optimize two inputs Hammerstein model,establish the main steam pressure Laguerre-Fuzzy Hammerstein identification,which solved the problem of low main steam pressure system identification accuracy caused by strongly nonlinear,large time delay,multivariable coupling,uncertainty and parameter time-varying,so that improved the control performance of predictive controller.4)Supercharged boiler control system includes fuel flow control loop and air flow regulation loop,and how to guarantee the two control loops coordinated operation is the key of the combustion control system.In this paper,the cascade control mode is adopted,of which the air flow control loop using the switching control strategy based on novel Petri network,and fuel flow regulation loop using a nonlinear predictive control algorithm based on normalized two inputs Hammerstein model and Laguerre-Fuzzy Hammerstein model separately.The proposed control strategy was analyzed based on the simulation model,and the results show that the proposed supercharged boiler combustion control strategy can more quickly adjust the main steam pressure in stable condition,with small oscillation amplitude,and guarantee the power balance and the system safety of turbocharged.Under the condition of drum water level and steam flow disturbance,the proposed control strategy can quickly adjust the main parameters of the system to stable value,which proves the effectiveness of the proposed control strategy.