Steam Generator Water Level Research Articles

The “regulation resonance” phenomenon in control systems and optimization schemes

Steam generator water level control incorporates the system that controls the speed of the main water feed pump and the one that controls the degree to which the main water feed valve is open. Although these two control systems are set independently, they have a reciprocal influence. A key problem is that, in the actuator for the regulation of the two systems, the regulated variables tend to oscillate with a relatively large amplitude even under stable conditions. In this paper, a pervasive regulating resonance phenomenon is inspected and analyzed by means of simulating the real working conditions. And using a mathematical model of the main water feed flow, it reveals that the two factors which directly cause the regulation resonance phenomenon are the frequency characteristics of the control system and the phase difference. On the basis of this, three potential optimization schemes have been proposed: the optimization of the regulation parameters; changing the phase difference; and setting a regulation dead-band which can improve the stability of the control system.

The preview control of a class of linear systems and its application in the fault-tolerant control theory

ABSTRACTIn the fault-tolerant control theory based on model following control, the desired signal of the control system is the output of a reference system. This paper is concerned with the design of the preview controller for a class of fault systems. A composite vector is introduced by including error vector, fault system state vector and reference system state vector. Then, we derived an augmented system from the known system equation, in which the reference input has equal status with the desired signal in the traditional preview control theory. Therefore, we can use the known theory to design the preview controller for the augmented system, then the preview controller of the original fault system can be obtained by the integration method. This paper strictly discusses the connection between stabilisation and detectability of the augmented system and the corresponding characteristics of the original system. Finally, by applying this theory to a real steam generator water level control system, it is found that the actions of the reference input preview and the fault signal preview can effectively eliminate the effect of the fault signal on the water level of the steam generator. The simulation shows the effectiveness of the controller designed.

Fractional order PID control of steam generator water level for nuclear steam supply systems

Abstract The main part of nuclear powered system is the nuclear steam supply system (NSSS) to produce the steam needed for electricity or cogeneration. The NSSS mainly contains the fission reactor, based on pressurized water reactors or small modular reactors, and the steam generator. One of the most important control strategies in the NSSS is water level regulation to keep the water level of the steam generator around programmed setpoint because violation of the level jeopardizes the plant availability in making the electricity and supplying the heat for industrial applications. The appearance of fractional calculus made it possible to realize the control design requirements in optimum and efficient ways. In this paper, we proposed a gain scheduled Fractional order PID (FOPID) control system for steam generator level control system in entire operating range. Nelder-Mead tuning strategy which takes into account the desired gain- and phase- margin with integral time absolute error (ITAE) performance index has been devoted to adjust the FOPID parameters. Simulation results indicate that the new control system can enhance the transient response in contrast to the conventional PID. The performance comparison of the FOPID regulator with the classical PID shows that the fractional controller has huge superiority which is comparable with the advanced quantitative feedback theory (QFT) controller. The Nyquist stability analysis is also provided to demonstrate the favorable robust stability of the gain scheduled FOPID controller over the wide range of operating conditions.

Controller tuning constants for the Advanced Power Reactor 1400 Feedwater Control System based on Ms-Constrained Integral Gain Optimization Method

Failure to control the steam generator (SG) water levels causes unexpected shutdowns in the Advanced Power Reactor (APR) 1400 nuclear power plants. This impacts maintenance, operational life, and safety critically. Therefore, it is vital to stabilize the SG water level at different power levels, particularly at low powers, by improving the performance of the proportional integral (PI) controller in the Feedwater Control System (FWCS). The PI controller designed using Ms-Constrained Integral Gain Optimization (MIGO) mitigated this problem significantly. In order to design this PI controller for the FWCS, the SG model was developed as a process model with a system identification algorithm in MATLAB. The algorithm processed data sets obtained from the thermal-hydraulic model by the Safety and Performance Analysis Code (SPACE). The MIGO and the Ziegler-Nichols methods were each used to produce a design for the PI controller, and the controllers were compared. Simulations were run in MATLAB for resulting designs. The PI controller designed by the MIGO is more stable than the controller using the Ziegler-Nichols approach. Finally, the PI MIGO controller was applied to an overall schematic block diagram of the FWCS. The simulations of the diagram in MATLAB Simulink demonstrate the PI MIGO controller offers superior control and enhanced robustness in the FWCS.

Thermal-hydraulic analysis of VVER-1000 residual heat removal system using RELAP5 code, an evaluation at the boundary of reactor repair mode

Removing the residual heat from a nuclear reactor is an important safety aspect of thermal hydraulic analysis. In this study, a typical VVER-1000 reactor residual heat removal system has been evaluated using RELAP5 thermal hydraulic loop code during cool-down. Reactor cooling down starts from hot state temperature and then continues to the cool-down stages with 130°C and 70°C, respectively. The second stage of cooling down is the boundary of the reactor repair condition. Main cooling pump head, steam generator (SG) water level, system pressure, the level of coolant in the pressurizer (PRZ), and the temperature of fuel element are examined in a steady state condition. PRZ level, primary circuit and secondary circuit pressure/temperature, and SG water level are evaluated during 32,000s after cool-down scenario. By comparison, it concluded that the results of RELAP5 code are in agreement with plant experimental data and final safety analysis report (FSAR). Thus, it is proved that the studied reactor is capable to remove the residual heat generated during shutdown. Moreover, RELAP5 is properly recommended for analysis of the VVER-1000 pressurized water reactor during cool-down.

浮动核电站给水系统瞬态分析

基于浮动核电站主给水系统，利用Flowmaster仿真软件建立了从除氧器出口至蒸汽发生器出口的给水系统模型。对给水系统四种瞬态过程中蒸汽发生器的水量变化进行分析：额定工况下一台给水泵跳闸，备用泵连锁启动；额定工况下一台给水泵跳闸，备用泵连锁启动失败；带零负荷时主给水调节阀故障全开；带满负荷时主给水调节阀故障全开。仿真结果表明，在给水泵切换瞬态工况下，蒸汽发生器的失水量在要求的范围内，不会触发反应堆跳停。并且根据瞬态工况的蒸汽发生器上水量的变化曲线，得到了保守的给水流量值作为核岛安全分析的输入，确保这些瞬态工况下堆芯不发生DNB。 Based on the floating nuclear power plant main water feeding system, the water feeding process model from the outlet of deaerator to the outlet of the steam generator is established by using a one-dimensional fluid simulation software Flowmaster. The change of water quantity of steam generator in four transient processes of water supply system is analyzed, includes: a water pump trip in rated state, and standby pump interlock start; a water pump trip in rated state, and standby pump interlock start; main feed-regulating valve is in full open due to failure under no load; main feed-regulating valve is in full open due to failure under full load. The simulation results show that: steam generator water level changes within the scope of the requirements under the feed pump switching transient conditions, which cannot trip the reactor. And according to steam generator water supply curves under the transient conditions, the conservative water flow value is obtained, which is an input to the nuclear island safety analysis, and to make sure the reactor core do not departure from nucleate boiling under these transient conditions.

Predictive Trip Detection for Nuclear Power Plants

This paper investigates the use of a Kalman filter (KF) to predict, within the shutdown system (SDS) of a nuclear power plant (NPP), whether safety parameter measurements have reached a trip set-point. In addition, least squares (LS) estimation compensates for prediction error due to system-model mismatch. The motivation behind predictive shutdown is to reduce the amount of time between the occurrence of a fault or failure and the time of trip detection, referred to as time-to-trip. These reductions in time-to-trip can ultimately lead to increases in safety and productivity margins. The proposed predictive SDS differs from conventional SDSs in that it compares point-predictions of the measurements, rather than sensor measurements, against trip set-points. The predictive SDS is validated through simulation and experiments for the steam generator water level safety parameter. Performance of the proposed predictive SDS is compared against benchmark conventional SDS with respect to time-to-trip. In addition, this paper analyzes: prediction uncertainty, as well as; the conditions under which it is possible to achieve reduced time-to-trip. Simulation results demonstrate that on average the predictive SDS reduces time-to-trip by an amount of time equal to the length of the prediction horizon and that the distribution of times-to-trip is approximately Gaussian. Experimental results reveal that a reduced time-to-trip can be achieved in a real-world system with unknown system-model mismatch and that the predictive SDS can be implemented with a scan time of under 100ms. Thus, this paper is a proof of concept for KF/LS-based predictive trip detection.

REDUCED ORDER MODEL OF U-TUBE STEAM GENERATOR AND APPLICATION OF FUZZY AND LQR IN ITS LEVEL CONTROL

The water level of the U-tube steam generator (UTSG) in a nuclear power unit, which is an important process parameter, must be maintained in a safe range whether the unit is working under fixed or variable conditions. In this paper, a higher order UTSG model derived from the state equations is reduced using Balanced Truncation technique. Two controllers using Fuzzy logic and LQR techniques have been designed for the reduced UTSG model to control its water level. Comparison of these two controllers has also been shown through the simulation results. Also, a comparative analysis of the reduced order model and a previously developed UTSG model is presented by simulating both UTSG models with Fuzzy Logic and LQR techniques and the results are compared.

A robust estimator-based optimal algebraic approach to steam generator feedwater control system

Feedwater control systems are used to maintain the steam generator water level within prescribed narrow limits and to provide constant supply of steam during power demand variations. Current feedwater control systems are often found to be unsatisfactory during startup and low power operations. A robust nonlinear estimator-based optimal algebraic control is developed for feedwater control systems to solve the water level tracking problem during power demand variations. It is shown that the proposed control provides an optimal and robust water level tracking with a single automatic controller over the complete range of power operations in the presence of plant uncertainties and noisy measurements.

Quasi-min-max Fuzzy MPC of UTSG Water<newline/> Level Based on Off-Line Invariant Set

In a nuclear power plant, the water level of the U-tube steam generator (UTSG) must be maintained within a safe range. Traditional control methods encounter difficulties due to the complexity, strong nonlinearity and “swell and shrink” effects, especially at low power levels. A properly designed robust model predictive control can well solve this problem. In this paper, a quasi-min-max fuzzy model predictive controller is developed for controlling the constrained UTSG system. While the online computational burden could be quite large for the real-time control, a bank of ellipsoid invariant sets together with the corresponding feedback control laws are obtained by off-line solving linear matrix inequalities (LMIs). Based on the UTSG states, the online optimization is simplified as a constrained optimization problem with a bisection search for the corresponding ellipsoid invariant set. Simulation results are given to show the effectiveness of the proposed controller.

A class of general transient faults propagation analysis for networked control systems

Transient faults are a dominant kind of threat to system safety in networked control systems (NCSs) due to their high occurrence rate and wide variety. However, they are hardly detected accurately in NCSs because of their unpredictable nature and short duration. Hence, fault propagation analysis (FPA) has become a bottleneck issue for fault-tolerant control in NCSs, which is used to analyze the fault effects and identify the approximate zone where transient fault occurred. In this paper, an innovative ontology-based FPA approach (ontologyFPA) is proposed to analyze transient fault propagation effects in NCSs. From the view of object-centered ontology, function, behavior, and structure models are built to reflect system abstraction hierarchies, and fault propagation effects and traces are identified from behaviors to functions through the mapping relationships of abstraction models. From the view of system-centered ontology, information-based workflows are employed to represent system independence in which fault propagation is investigated by excavating different effect traces among serial tasks in control loops. To illustrate the processes of propagation analysis, the application of ontologyFPA in a steam generator water level control system is presented. Finally, based on a unified simulation platform described by the architecture analysis and design language (AADL), two types of faults are injected to inspect the fault propagation processes between abstraction hierarchies, while another type is injected to investigate the processes in workflows. The results demonstrate that the proposed approach is effective in terms of identifying transient fault propagation effects and traces.

Support vector regression model based predictive control of water level of U-tube steam generators

A predictive control algorithm using support vector regression based models was proposed for controlling the water level of U-tube steam generators of pressurized water reactors. Steam generator data were obtained using a transfer function model of U-tube steam generators. Support vector regression based models were built using a time series type model structure for five different operating powers. Feedwater flow controls were calculated by minimizing a cost function that includes the level error, the feedwater change and the mismatch between feedwater and steam flow rates. Proposed algorithm was applied for a scenario consisting of a level setpoint change and a steam flow disturbance. The results showed that steam generator level can be controlled at all powers effectively by the proposed method.

Steam Generator Water Level Intelligent Control of PWR Nuclear Power Plant Based on Feed Water Regulation

Water level control of the steam generator is an important indicator of the safe operation of nuclear power plant. The traditional PID controller system has the disadvantages of large amount of overshoot, long adjusting time, etc. Steam generator has complex, nonlinear and time-varying characteristics. This article proposes the adopting the BP neural network intelligent control algorithm. The simulation experiments results indicated that: Comparing with traditional PID control it has smaller overshoot and shorter adjustment time, more ideal control effect c.

Application of the K-Means Immune Particle Swarm Optimization Algorithm in the Steam Generator Water Level Control

The Stability of SG water level plays an important role in the safety of nuclear power plants, but tuned the parameter of water level PID controller is hard. Proposed a novel algorithm, KIPSO, which tuning PID controller parameters. Determine the cluster centre through K-means value cluster algorithm, and take the cluster territory as the characteristic value of vaccine set, enhance the vaccine multiplicity. Updated vaccine extraction by self-adaptive method, improved the convergence and adaptability. Analyzed the algorithm robustness in detail, and gave the rule which the immunity selection parameter. The simulation results shows: compares with the PID controller whose parameters are tuned by ZN method, KIPSO have a smaller overshoot, a better stability, and a shorter adjustment time. The simulation results show that the proposed method is effective for tuning PID parameters.

The Application of Ecological Interface Design Methodology for Digitalized MCR in Nuclear Power Plant

Objective: This study proposes the application of Ecological Interface Design(EID) method that is effective for situation awareness in digitalized environment. Background: While cognitive interface design method such as Information Rich Display(IRD) is simply focused on existing information for user, EID method helps users" resource to be solved to higher abstraction task such as diagnostic and problem solving. Method: Using EID method based on Work Domain Analysis(WDA), it was analyzed and designed for Steam Generator(SG) Water Level control process in a digitalized Main Control Room of Nuclear Power Plant. Proposed EID example is evaluated through interviews by expert & operator. Results: The result of expert & operator showed that EID display might give an aid for operator"s decision. Conclusion: The results can reduce critical accidental damage that occurred due to cognitive load and so critical human error. Application: This study may be impact on situation awareness study for digitalized interface design.

Parameter Optimization of Steam Generator Feedwater Controller Based on Particle Swarm Optimization

The U-tube steam generator(SG), as the joint of primary and secondary circuits, is one of the crucial components in a PWR plant. Because of the swell-and-shrink phenomena, it is very difficult to control the water level of the steam generator. Presently the three-element controller in cascade configuration with two PID controller is widely use. But the determination of the six optimal PID parameters of the cascade controller is a major problem. This paper studies the application of the particle swarm optimization(PSO) methods in determining the parameters of cascade controller of SG water lever. The SG is modeled in Simulink and the PSO algorithm is implemented in MATLAB. Comparing with conventional PID parameter, the proposed method is more efficient in improving the step response characteristics while controlling the water level of SG.

The Application of Cognitive Interface Design Methodology for a Digitalized Main Control Room in Nuclear Power Plant

This technical study describes the application of Ecological Interface Design (EID) method that may improve operator performance in digitalized system environment such as main control room in next generation nuclear power plant. While cognitive interface design method such as Information Rich Display (IRD) is mainly focused on stereotyped information for the user, EID method helps users' mental resources to be allocated to tasks that process highly abstract information including diagnosis and situation assessment. However, the sophisticated and relationship-embedded EID displays may cease to be intuitive when many of them are presented without consistently designed common elements. This study aims at suggesting consistent elements of EID displays for a digitalized Main Control Room of Nuclear Power Plant taking the example of the control process of Steam Generator (SG) Water Level. The proposed EID displays were reviewed by domain experts and operators to conjecture how such EID displays might benefit the operator's decision making. The experience from this study indicates that situation awareness in digitalized interface design may be improved by appropriately designed visualization of abstract information and that operator may be aided by the represented dynamics in EID display.

The Steam Generator Water Level System Based on Nonlinear First Order ADRC Control

The Steam Generator with the characteristics nonlinear, time varying, and non-minimum phase whose water level will fluctuate significantly when it encounters inner disturbance or outside interference. For the above problem, the ADRC of steam generator will be designed in this article. Based on the dynamic characteristics of steam generator, equivalent the steam generator model to be the generalized first order system and establish control system based on nonlinear first order ADRC. The simulation results show that the proposed control strategy can achieve better control performance.

Performance assessment for the water level control system in steam generator of the nuclear power plant

The steam generator water level control system is the most important components of a nuclear power plant. The operating steam generator water level control system is increasingly recognized as a capital asset that should be routinely maintained and monitored. However, the control loop performance assessment is still an open problem; thus, the performance assessment technology will be brought into the steam generator water level control system in nuclear power plants. Performance assessment methods for the plant with stable and unstable zeros of two PI controller systems are developed at all specific power levels. The numerical examples will demonstrate the effectiveness of the proposed method.

Adaptive estimator-based dynamic sliding mode control for the water level of nuclear steam generators

Steam Generator (SG) is a crucial component of nuclear power plant. The proper water level control of a nuclear steam generator is of great importance in order to secure the sufficient cooling source of the nuclear reactor and to prevent damage of turbine blades. The water level control problem of steam generators has been a main cause of unexpected shutdowns of nuclear power plants which must be considered for plant safety and availability. The control problem is challenging, especially at low power levels due to shrink and swell phenomena and flow measurement errors. Moreover, the dynamics of steam generator vary as the power level changes. Therefore, it is necessary to improve the water level control system of SG. In this paper, an adaptive estimator-based dynamic sliding mode control method is developed for the level control problem. The proposed method exhibits the desired dynamic properties during the entire output tracking process independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness and stability. Simulation results confirm the improvement in transient response obtained by using the proposed controller.