Model predictive pressure control of steam networks

The control scheme of industrial power plants leads typically to a complex multivariable control structure with active constraints to be taken care of. Then Model Predictive Control method (MPC) handles multivariate control problems naturally and optimal control result is calculated considering actuator limitations and constraints of process variables. MPC is applied to control the pressure stability in a multilevel steam network. The system is demonstrated in a simulator environment. MPC can also be used as a convenient tool for analyzing and designing the structure of the steam network. A power plant simulator controlled by MPC helps to decide the location and the capacity of steam levelling components needed to stabilize the operation of the process.     

考虑汽蚀影响的给水泵仿真建模及实现

该文根据蒸汽动力装置模拟器的研制需求,讨论了考虑汽蚀影响的给水泵仿真建模和实现方法。蒸汽动力装置中使用的给水泵动态特性变化很大,给水泵作为变转速泵的特性模拟在整个蒸汽动力装置热工水力特性模拟中占有非常重要的地位。由于给水泵性能受汽蚀影响很大,因此考虑汽蚀对给水泵性能的影响对于提高模拟器在正常工况和事故工况下的仿真精度有很大意义。该文构建的模型形式简单,计算精度高,覆盖的给水泵运行工况宽。该文提出的仿真模型和数值方法对于同类型泵的仿真建模和计算分析具有一定的参考价值。     

Dynamic behaviour of material states in steam power plant control

The enormous price increase in petroleum and the limited reserves of other fossil fuels have resulted in the increased use of nuclear power plants for the basic load of electricity supply. Consequently, conventional steam power plants have been used to meet the variable and peak loads in electricity generation. The control of fast and large load changes is becoming more and more important for conventional power plant operations. An economical control of the nonstationary operation (start-up, shut-down and large load changes) is possible only by approaching and maintaining the maximum allowable values of the material state variables (temperature θ, strain ? and stress σ) at the critical points of the power plant components. To achieve this primary control goal, the dynamic behaviour of material states must be well understood. A direct measurement of the changes in material states especially due to thermal stresses, caused by temperature gradients, is not possible. The material states can be calculated, however, by means of mathematical models describing the nonstationary temperature distribution. The working fluid temperature, pressure and mass flow rate are the input variables for these mathematical models. This paper presents a linear mathematical model for the investigation of the dynamic behaviour of material states. Another mathematical model is also developed for calculating the thermal stresses for large temperature and load changes. Thus, the steam generator models so far describing only the states of the working fluid can be extended to the material states. The basic idea is demonstrated for an insulated thick wall tube containing a working fluid. The simulation of the mathematical models is performed.     

AGC及汽温优化控制系统在330MW级火电机组的应用

首先提出了330MW亚临界机组AGC及汽温优化控制方案,其次详细论述了先进优化控制策略的特点和相关调试方案,最后介绍了先进优化控制系统在330MW级火电机组上的成功运用以及取得的实际效果,解决了火电厂汽温变负荷工况参数不稳的问题并提高了机组的经济性,为新型先进控制系统推广应用提供了技术参考。     

Repetitive control of tubular heat exchangers

Effective operation of heat exchangers involves optimum control of the fluid outlet temperature. Several ideas have been proposed in the literature to cope with intrinsic resonance dynamics aimed at widening the bandwidth of the closed-loop system to achieve fast, well-damped responses in controlling the outlet fluid temperature by means of the steam temperature. This is also the main purpose of this article, in which the use of a repetitive control scheme is proposed to take resonance dynamics into account when residence time is variable, as in this case the control variable is the fluid flow rate and not the steam temperature. The scheme is based on a model of the tubular heat exchanger dynamics in which the explicit terms of resonance are cancelled out by the controller. Simulation results are provided both for a typical tubular heat exchanger and for a special sort of heat exchanger, the distributed collector field of a solar power plant.     

核电站蒸汽发生器水位控制系统的仿真研究

研究核电站蒸发器水位控制优化问题,由于蒸汽发生器是核电站中最重要设备之一,水位控制对核电站的安全运行起着决定性的作用,并要求系统稳定运行,快速响应。针对蒸汽发生器是一个高度复杂、非线性、时变的系统,传统的串级PID控制等控制方法难以取得满意的控制效果,把自抗扰控制方法引入蒸汽发生器水位的串级控制系统中,解决传统PID快速性和超调的矛盾,且能够动态补偿对象模型的内扰和外扰。另外,自抗扰控制器的参数较多且参数难以整定,采用混沌搜索的粒子群混合优化算法来对优化选择参数进行仿真。仿真结果表明,改进方法的鲁棒性和控制品质优于传统的串级PID控制方法,方法的可行性和有效性。     

Neuro-fuzzy generalized predictive control of boiler steam temperature

Power plants are nonlinear and uncertain complex systems.Reliable control of superheated steam temper-ature is necessary to ensure high efficiency and high load-following capability in the operation of modern power plant.A nonlinear generalized predictive controller based on neuro-fuzzy network(NFGPC)is proposed in this paper.The proposed nonlinear controller is applied to control the superheated steam temperature of a 200MW power plant.From the experiments on the plant and the simulation of the plant,much better performance than the traditional controller is obtained.     

Neuro-fuzzy generalized predictive control of boiler steam temperature

Power plants are nonlinear and uncertain complex systems. Reliable control of superheated steam temperature is necessary to ensure high efficiency and high load-following capability in the operation of modern power plant. A nonlinear generalized predictive controller based on neuro-fuzzy network (NFGPC) is proposed in this paper. The proposed nonlinear controller is applied to control the superheated steam temperature of a 200MW power plant. From the experiments on the plant and the simulation of the plant, much better performance than the traditional controller is obtained.     

神经元解耦控制方案在火电厂球磨机FCS中的设计

给出了一种由神经元和静态解耦网络相结合的针对火电厂球磨机现场总线控制的方案。并在此基础上将此控制方案应用于火电厂球磨机的现场总线控制系统的设计和开发，论证了该种控制方案在FCS控制系统中的可行性，并详细阐述了该控制方案在FCS上位监控级和现场级的实现方法和过程。从实时仿真和现场运行的结果看，该种控制方案在FCS中实现可以取得令人满意的控制效果。     

基于PROFIBUS总线的大型火电厂分布式控制系统设计

利用现场总线支持下的分布式控制技术是目前数字化火电厂得以实现的重要途径;论述PROFIBUS总线基本特征的基础上,设计了一种以现场级的PROFIBUS总线为基础的大型火电厂分布式控制系统,并对控制系统的各个部分功能和作用进行了阐述和说明,提出了具体的实现方法。同时讨论了目前以PROFIBUSPROFIBUS总线为基础的火电厂控制系统方案设计和实现过程中应解决的关键问题;最后,结合陕西省杨陵热电厂一号机组的应用实例说明了PROFIBUS总线作为电厂中现场级网络的可行性。     

一种复合控制器在过热汽温中的应用研究

在电厂中,必须严格控制过热器出口蒸汽温度,蒸汽温度过高或过低,都将给安全生产带来不利影响。针对过热汽温被控对象的特点,充分利用模糊控制的动态特性好和PID调节能消除静态偏差的特性,设计了一种带自调整因子的模糊控制器,研究了Fuzzy-PID复合串级控制在电厂过热汽温控制系统中的应用,该复合控制器的切换采用一种简单的基于偏差量的模糊切换方法。仿真结果表明,Fuzzy-PID复合串级控制系统具有更好控制品质。     

汽包锅炉的一种非线性串级控制设计

电厂锅炉的非线性和大延迟时间常数等是影响其控制品质主要因素。针对这些问题,提出一种非线性串级控制设计方案,一方面采用非线性补偿能够抵消锅炉的非线性的影响,另一方面采用串级控制能够提高锅炉的动态响应速度。在控制设计中,选择锅炉汽包压力为副控制对象、主蒸汽压力为主控制对象构成串级控制系统。仿真研究表明,在大范围变负荷运行条件下,所设计的机组控制系统具有良好的控制品质并能够有效地提高锅炉的响应速度。     

Modelling and dynamic simulation of a parabolic trough power plant

Investigational dynamic simulations of an existing 50 MW_el parabolic trough solar thermal power plant in Spain are carried out during clear days and slightly cloudy periods. This work is the first research, which presents a detail dynamic model of a parabolic trough power plant. Besides the thermal energy storage system and solar field, the developed model describes the heat transfer fluid and steam/water paths in detail. Advanced control circuits, including drum level, economiser water bypass, attemperator and steam bypass controllers are also included. The parabolic trough power plant is modelled using Advanced Process Simulation Software (APROS). The comparison between the simulation results and measured data is documented, showing a reliable prediction of the real behaviour of the investigated solar power plant. The validated model offers a possibility for accurate simulation of further operation processes of the real plant.     

Intelligent coordinated controller design for a 600 MW supercritical boiler unit based on expanded-structure neural network inverse models

Under present widespread automatic generation control (AGC) centered on regional power grid, a large-capacity coal-fired supercritical (SC) power unit often operates under wide-range variable load conditions. Since a SC once-through boiler unit is represented by a typical multivariable system with large inertia and non-linear, slow time-variant and time-delay characteristics, it often makes the coordinated control quality deteriorate under wide-range loading conditions, and thus influences the unit load response speed and leads to heavy fluctuation of the main steam pressure. To improve the SC unit’s coordinated control quality with advanced intelligent control strategy, the neural-network (NN) based expanded-structure inverse system models of a 600 MW SC boiler unit were investigated. A feedforward neural network with time-delayed inputs and time-delayed output feedbacks was adopted to establish the inverse models for the load and the main steam pressure characteristics. Based on the model, a neural network inverse coordinated control scheme was designed and tested in a full-scope power plant simulator of the given SC power unit, which showed that the proposed coordinated control scheme can achieve better control results compared to the original PID coordinated control.     

NSG水位神经自适应PID控制与仿真研究

核动力蒸汽发生器(NSG)是一个高度复杂的非线性时变系统。由于蒸汽发生器在瞬态、启动和低功率下的“收缩”与“膨胀”现象引起的逆动力学效应,使蒸汽发生器的水位控制变得复杂。本文针对传统的核动力蒸汽发生器水位PID控制方法存在的缺点,将神经网络方法与PID控制的结构结合起来,提出了核动力蒸汽发生器水位神经自适应PID控制方法。采用BP学习算法调整控制器神经网络的连接权值,实现了控制器参数的在线整定。仿真研究表明,所设计的控制器具有良好的控制性能,且结构简单,易于实现。     

基于模糊-PID的汽轮机转速控制系统

船用核动力装置机动性要求较高,采用直流蒸发器的船用核动力装置,多参数问具有较强的耦合关系,各主要控制器之间应能相互协调。汽轮机转速如采用常规的PID调节不能较好地满足控制需求。本文设计了汽轮机转速模糊PID双模控制系统,并对蒸汽压力具有协调控制功能,利用模糊控制的快速动态响应和PID控制的稳态性能,来实现汽轮机转速快速跟踪、稳定控制的要求。仿真试验表明该控制系统响应时间和稳态精度都有明显改善。     

Size scale effects on cavitating flows through microorifices entrenched in rectangular microchannels

Cavitating flow of deionized water through various microorifices and microchannels has been investigated. Multifarious cavitating flow patterns, including incipient, choking and supercavitation have been detected. Effects of microorifice and microchannel size on cavitation have been discussed and results indicate the existence of strong size scale effects. Incipient and choking cavitation numbers are observed to increase with the area ratio between the microorifice and the microchannel while the orifice discharge coefficient plummets once cavitation activity erupts. Additionally, for a fixed microchannel width, the incipient and the choking cavitation numbers rise with the ratio between the hydraulic diameters of the microorifice and the microchannel. In addition, velocity and pressure effects on cavitation have been investigated for several microorifices and the observed trends have been compared with established macroscale results. Furthermore, the flow patterns encountered at choking and supercavitation are significantly influenced by the microorifice and microchannel size. Flow rate choking occurs irrespective of the inlet pressures and is a direct consequence of cavitation inside the microorifice. The predicted choked cavitation number is always higher than the experimental data. This discrepancy is suspected to be the result of exceedingly small residence time for nuclei growth and the ability of the liquid to withstand low pressures at such scales. Flow and cavitation hysteresis is observed but its effects are more pronounced for the smallest microorifice.     

Optimization of boiler control to improve the load-following capability of power-plant units

The capability to perform fast load changes has been an important issue in the power market, and will become increasingly more so due to the increasing commercialization of the European power market. An optimizing control system for improving the loadfollowing capability of power-plant units has therefore been developed. The system is implemented as a complement, producing control signals to be added to those of the existing boiler control system, a concept which has various practical advantages in terms of implementation and commissioning. The optimizing control system takes account of the multivariable and load-dependent nonlinear characteristics of the boiler process, as a scheduled LQG controller with feedforward action is utilized. The LQG controller improves the control of critical process variables, making it possible to increase the load-following capability of a specific plant. Field tests on a 265 MW coal-fired power-plant unit reveals that the maximum allowable load gradient that can be imposed on the plant, can be increased from 4 to 8 MW/min.     

电厂过热汽温混合模糊控制仿真分析

简要介绍火电厂过热汽温控制对象的特点,并根据其特点,提出双模糊控制器+PID的混合模糊控制方案,并应用MATLAB的SIMULINKToolbox对系统进行了仿真分析。仿真分析的结果表明,采用混合PID模糊控制的效果明显优于常规PID控制以及仅用模糊控制器进行控制。     

火电厂主气温系统的继电反馈多模型控制

针对火电厂变负荷机组主汽温系统时变和非线性的特点，提出了基于继电反馈的多模型控制算法;首先利用继电反馈的方法，对若干典型工况点建立的固定模型设计子控制器;在运行过程中，利用多模型控制根据系统工况的变化选择相应的控制器以保证系统的控制性能，仿真结果表明应用该方法建立的控制系统具有良好的控制品质和较强的自适应能力。