【作者】 卓旭升；

【导师】 周怀春；

【作者基本信息】 华中科技大学 ， 热能工程， 2008， 博士

【摘要】 电网用电量的高峰和低谷的频繁变动要求联网发电的燃煤火电机组的运行工况不断地改变。在这个过程中,机组展现出的强非线性、耦合性及参数的时变性等常常造成现有的控制系统性能下降,有时会造成控制系统失灵而被迫采用手工调节,严重的影响了机组运行的安全性和经济性。应对措施之一就是引进适应性强的高性能控制系统。为此,研究机组的动态特性并建立模型是研发高性能控制系统成功的关键。过热系统是大型燃煤机组中的重要组成部分,其输出的主蒸汽压力和温度是要控制的主要参数。本文先提出一种能够确定具有两个独立自变量函数关系式的新方法-双线性拟合法,并予以证明。然后,从过热蒸汽的热力特性入手导出过热蒸汽的比焓函数和密度函数的简化计算式。在此基础之上,依据质量平衡和能量平衡原理建立了过热器的数学模型,揭示了蒸汽流量、吸热量和减温器喷水流量对主蒸汽压力和温度动态特性的影响。燃料系统的延迟时间、动态系数以及蒸发系统的热惯性是影响锅炉响应负荷指令变化速度的主要因素。本文依据守恒定律建立了这两个系统的模型。利用炉膛辐射能信号能够及时反映燃料燃烧释放出的热量的特点,可以确定燃料系统的延迟时间及高温段过热器吸热量;燃料系统的动态系数由辨识方法确定;通过分析和拟合将复杂的蒸发系统热惯性表达式转化为简便的计算式。利用一台300MW燃煤机组运行数据和计算对de Mello的简化模型中汽包出口蒸汽流量的计算式进行了修正。在验证模型方面,本文仅用实际机组变负荷运行条件下测量的数据。这样,可以避免外加试验信号对机组正常运行的干扰。将适当的非线性控制方法引入到火电机组的控制设计中对提高机组控制系统的性能大有裨益。微分几何非线性控制和非线性模型预测控制是两种令人感兴趣的控制方法,它们适于处理运行条件变化大的非线性过程的控制问题。本文利用微分几何非线性控制方法对一台300MW燃煤机组非线性模型进行了解耦线性化控制设计。在设计方案中,考虑到实际控制执行机构具有幅值约束条件的限制,增加了指令处理器的设计,通过减缓指令的轨迹以使控制约束条件得到满足。由于非线性机组模型被解耦线性化,因此,该控制系统能够使机组在大范围内跟随指令要求且保持稳定。基于泰勒级数展开式的非线性模型预测控制方法可以导出解析形式的控制规律,避免了在线滚动优化的计算负担。因而,在复杂的过程控制中具有明显的优点。本文将这种控制方法引入到一台燃油火电机组的控制研究中。为了克服机组的某一状态变量不可测量的缺陷,将控制器的实现形式采用为模型状态反馈内模控制结构。这样,一方面可以避免设计非线性观测器的麻烦,另一方面也增强了控制系统的抗干扰能力。通过证明发现,该设计方案具有一定的鲁棒性。更多还原

【Abstract】 To match frequent varying electricity demands from the power network, the grid-connected generate units in the coal-fired power plants have to be operated over wide varying operation range. During the course, the severe nonlinearity of boiler-turbine unit, the coupling variables and time-varying parameter et al usually degrade the performance of the existing control system, sometime can confuse it and the manual regulation is switched, then the unit operation safety and economy can be badly decreased. One of the suitable methods to overcome these challenges is to develop the high-performance control system. Investigating the dynamic of the unit and modeling it are the key basal work for developing the high-performance control system.The super-heater is a significant part of the large-scale coal-firing power generating unit, and the steam pressure and temperature out of it are the major objective parameters. In the study, firstly, a new bilinear fit method which can determine the expression of the two variables function is developed and proved, then the thermodynamic property of superheated steam is viewed and the simple expressions of the enthalpy and density of superheated steam are deduced through bilinear fit. In the work, the model of super-heater is set up based on first-principle equations (mass, energy balance et al). Influence of steam mass flow rate, heat flux rate and desuperheating spray water mass flow rate on the dynamic performance of superheated steam pressure and temperature is shown in the model.The delay time constant and dynamic coefficient of the fuel system and the thermal inertia of the evaporator in boiler are the major elements which affect the boiler to response to the load command. In the study, the dynamic model of the fuel system and evaporator are set up based on the mass and energy balance equations. The furnace radiation energy signal, displaying the heat energy from fuel combustion immediately, is applied to determine the delay time constant in the fuel system and the heat flux rate to the high temperature segment super-heater. And the dynamic coefficient in the fuel system is determined by the identification technique. By analyzing and fitting, the complicated expression of the thermal inertia of the evaporator is substituted by a simple one. The expression of steam mass flow rate out of drum in boiler in de Mello’s simple model is revised and validated by using the operating data from a 300MW coal-fired generate electricity unit. Finally, the model can be validated through only using the data from a 300MW coal-fired generation unit operating over a varying operation range, and the trial is not needed. Hence, large disturbance on the normal operation of the generation electricity unit is avoided.It is very helpful to improve the performance of unit’s control system that the suitable nonlinear control methods are introduced into the control design of boiler-turbine unit. The differential geometric control and nonlinear model predictive control are of interest two methods which can be applied to the control design for nonlinear process operating over wide operation range. In the study, the differential geometric approach is applied to design the control system of a 300MW coal-fired generation electricity unit. To meet the saturation constraints on actuator, a reference governor is designed in the control scheme to make the reference trajectories sluggish. Since the unit’s model is decoupled and linearized exactly over a wide operation range, the control design can achieve tracking performance in the power output and the control system is stable.Based on Talyor series expansion to certain order, the nonlinear model predictive control approach can deduce an analytic controller and the online optimization computation burden on a receding horizon is avoided. Therefore, the control method has the obvious strongpoint in complex nonlinear process control. In the study, the control method is introduced into the control design for an oil-fired boiler-turbine unit. To solve the issue of an unmeasurable state variable in the unit, the controller is implemented in the model state feedback form, a sort of internal model control structure. In this way, on the one hand, the complex design of a nonlinear observer isn’t avoided; on the other hand, the control system’s capability to reject disturbance is strengthened. The proof shows the designed control system is robust.更多还原