Nolinear Control For Boiler-Turbine Coordinated Problems In Large Scale Ships’ Steam Power Plant With Double Supercharged Boilers

Shipping maximization is the main trend in the development of ships,which requires more powerful marine power plants to match it.From either technical or economic point of view,although there are many kinds of marine power plants,steam power plant is still the first choice of large marine power plants.In China,the technology related to large marine steam power plant is relatively backward and the relevant experience is not enough.Therefore,carrying out in-depth research of large marine steam power plant has practical implications.Most of the current research studies on the boiler-turbine coordinated control strategy for the marine steam power plant consider the strategy as an independent topic,which falls short of the organic connection with the control strategies of other loops in the steam power plant.To build a comprehensive control system for large ship-scale marine steam power plants with boiler-turbine coordinated control as the main body,the research of this topic falls into the following parts:Firstly,modeling research is carried out for modeling of large-scale marine steam power plants.For the modeling of the fuel flow system,the relationship in which between the pressure in the system changes with fuel volume in the oil circuit is given.For the modeling of the air flow system,another relationship is build,in which the pressure and temperature of air in the mezzanine chamber changes nonlinearly with the air flow in the trubo-compressor,main air outlet valve and bypass air outlet valve.In the modeling of the main steam pressure of the double supercharged boiler unit,the disturbing effect of the temperature fluctuation of superheated steam inside the marine supercharged boiler on the steam pressure when the working condition changes is explained,and the accuracy of the main steam pressure model is improved.For the marine steam power propulsion system,a rotational speed quadratic homeomorphic mapping modeling method is proposed to replace the speed with the speed quadratic that has homeomorphic mapping relationship with the speed as the state variable of the marine steam power propulsion system model.While the traditional model cannot be used to simulate the speed passing through the zero point of the marine steam power propulsion system in the process of ahead and astern switching,this method realized full working condition simulation.Secondly,to analyze the influence of the boiler-turbine coordinated control by other control loops in the device,the air-fuel joint control problem is investigated.The air pressure controller in the mezzanine chamber of the air flow system is designed to improve the performance of the whole air flow control system.In view of the problems that the air flow system and fuel flow system are isolated from each other and the dynamic characteristics of the air flow system are slower than those of the fuel flow system in the supercharged boiler of the marine steam power plant,the joint air-fuel flow control strategy is proposed for the marine supercharged boiler based on information interaction fuzzy adaptive PID control algorithm with variable universe.As a result,it solved the problem that the ratio of air flow to fuel flow does not fall within the optimal combustion interval during the change of operating conditions,ensured that the combustion in the furnace is in the optimal state,and improved the fuel energy utilization of the marine supercharged boiler.These all are beneficial for energy saving and emission reduction.Thirdly,for the main steam pressure control of the double supercharged boiler,a dual closed-loop nonlinear control PID strategy is proposed based on genetic algorithm optimization,with the inner loop controlling the superheated steam pressure and the outer loop controlling the main steam pressure to stabilize the internal heat load state of the supercharged boiler.At the same time,in response to the interference problem of superheated steam temperature fluctuation on the main steam pressure control of the marine double supercharged boiler unit in the process of changing working conditions,an adaptive composite degree based SVM-PID superheated steam temperature control strategy is adopted to tackle complex problems such as uncertainty,system time lag and nonlinear characteristics in the convective heat transfer process of superheated steam.On top of that,by stabilizing the superheated steam temperature,improvements are made on the uneven distribution of main steam temperature and mass in the steam header of the double supercharged boiler unit.This reduced the disadvantages of the main steam pressure control in the double supercharged boiler.Subsequently,the application of model predictive control in the rotational speed control of marine steam power propulsion system is studied.With respect to the nonlinear characteristics of the marine steam power propulsion control system,a flexible reference PSO intelligent optimization model predictive control strategy is proposed.Among that,PSO intelligent optimization algorithm imposed optimal control over the nonlinear characteristics of marine steam power propulsion control system and the non-convex optimization problem caused by different ahead and astern models corresponding to the ahead and astern conditions of the system.The flexible algorithm can ensure that the optimal solution satisfies the constraints of the control input,thus achieving optimal control and saving energy.Finally,in view of the problem of imbalance between the steam production of the supercharged boiler unit and the steam consumption of the propulsion system in the boiler-turbine coordinated control of the steam power plant of the double supercharged boiler of a large-scale marine,a first-order ε proximity type PSO intelligent optimization nonlinear model predictive control strategy is proposed."Model prediction" enabled the double supercharged boiler unit to prepare for the change of operating conditions in advance,and eliminated the coupling effect between the main steam pressure and the propulsion system.The introduction of superheated steam pressure in the state variables stabilized the internal heat load state of the double supercharged boiler,and the introduction of the model state derivative term in the objective function made the system output smoother.The proposed first-order ε proximity PSO intelligent optimization nonlinear model predictive control strategy further eliminated the imbalance between the steam production of the supercharged boiler unit and the steam consumption of the propulsion system through simulation,as opposed to the IBICDC intelligent decoupling control strategy in this paper,and exerted better control over the boiler-turbine coordinated control issue of the marine steam power plant.