Plant Control System Research Articles

Advanced Control System for Grid-Connected SOFC Hybrid Plants: Experimental Verification in Cyber-Physical Mode

This paper presents a model predictive controller (MPC) operating a solid oxide fuel cell (SOFC) gas turbine hybrid plant at end-of-life performance condition. Its performance was assessed with experimental tests showing a comparison with a proportional integral derivative (PID) control system. The hybrid system (HS) operates in grid-connected mode, i.e., at variable speed condition of the turbine. The control system faces a multivariable constrained problem, as it must operate the plant into safety conditions while pursuing its objectives. The goal is to test whether a linearized controller design for normal operating condition is able to govern a system which is affected by strong performance degradation. The control performance was demonstrated in a cyber-physical emulator test rig designed for experimental analyses on such HSs. This laboratory facility is based on the coupling of a 100 kW recuperated microturbine with a fuel cell emulation system based on vessels for both anodic and cathodic sides. The components not physically present in the rig were studied with a real-time model running in parallel with the plant. Model output values were used as set-point data for obtaining in the rig (in real-time mode) the effect of the fuel cell system. The result comparison of the MPC tool against a PID control system was carried out considering several plant properties and the related constraints. Both systems succeeded in managing the plant, still the MPC performed better in terms of smoothing temperature gradient and peaks.

The Fastest Response Algorithm for Thermal Plants with a Time Delay: Application in a Hybrid System Containing a PID Controller and an Automatic Tuning Unit

The article discusses matters concerned with improving the performance of automatic closed-loop control systems of thermal plants with a time delay in responding to a change in the setpoint. The improvement is achieved by applying the fastest response algorithm (FRA) according to the Pontryagin maximum principle and using linear prediction of the controlled variable. It is shown that, during operation with switching the maximum control outputs applied to a plant with a time delay, linear prediction is inefficient, and self-oscillations may occur in the system. The technical solution proposed for eliminating self-oscillations implies the use of a hybrid closed-loop control system comprising an FRA, a PID controller, and an automatic controller tuning (ACT) unit, which performs the function of determining the plant model parameters and optimizing the controller parameters. The actuator is considered as a proportional section that is used as part of the plant. The control limitations are related to the level of the control output applied to the plant. The ACT unit comprises accelerated controller tuning algorithms that use active plant identification methods based on analyzing the response to an impulse input and two cycles of the excited self-oscillations. These algorithms make it possible to determine four parameters of the second-order plant model with a time delay. The self-oscillations occurring in systems with the FRA and plants with a time delay are eliminated at the end of the transient by making a switchover to PID control. Four embodiment versions of a system with the FRA are analyzed, specifically, those with and without control output reversal and also with using the plant simulation model without a time delay that is obtained from the ACT operating in parallel with the plant. For practical embodiment of the MSRA as part of a hybrid system, it is recommended to use its version without control output reversal. Relations for calculating the controlled variable prediction coefficient in terms of the plant model parameters in a wide range are obtained. Two examples of using the hybrid system equipped with industry-grade controllers for a temperature control system are given: one with the electric heater power controlled using a pulse-width modulator and the other with a constant speed actuator.

Verification of safety critical and control systems of Nuclear Power Plants using Petri nets

Non-functional requirements play a critical role in designing variety of applications domain ranging from safety-critical systems to simple gaming applications. Performance is one of the crucial non-functional requirements, especially in control and safety systems, which validates the design. System risk can be quantified as a product of probability of system failure and severity of its impact. In this paper, we devise a technique to do the performance analysis of safety critical and control systems that helps to estimate the risk. The technique elaborates Petri nets to estimate performability to ensure system dependability requirements. We illustrate the technique on a case study of Nuclear Power Plant. The technique has been validated on its 17 safety critical and control systems.

Control of Solvent-Based Post-Combustion Carbon Capture Process with Optimal Operation Conditions

Solvent-based post-combustion carbon capture (PCC) is a mature and essential technology to solve the global warming problem. The high energy consuming issue and the flexible operation required by the power plants inquire about the development of effective control systems for PCC plants. This study proposes the optimal-based control approach that utilizes optimal set-point values for the quality controllers. The five optimal-based control schemes studied all employed L/G (liquid to gas ratio in absorber) as one quality control variable. Performance comparisons with a typical conventional control scheme are conducted employing a rate-based dynamic model for the MEA (monoethanolamine) solvent PCC process developed on a commercial process simulator. Compared to the typical control scheme, the optimal-based control schemes provide faster responses to the disturbance changes from the flue gas conditions and the set-point change of the CO2 capture efficiency, as well as better results in terms of IAEs (integral of absolute errors) of capture efficiency and reboiler heat duty during the stabilization period. LG-Tstr and LG-Tabs-Cascade are the best schemes. In addition to L/G, these two schemes employ the control of Tstr (the temperature of a stage of stripper) and a cascade control of Tabs (the temperature of a stage of absorber) (outer loop) and Tstr (inner loop), respectively.

Towards Design of Quasilinear Gurvits Control Systems

The design problem of control systems for nonlinear plants with differentiated nonlinearity is considered. The urgency of this problem is caused by the big difficulties of practical design of nonlinear control systems with the help of the majority of known methods. In many cases, even provision by these methods of just stability of equilibrium point of a designing system represents a big challenge. Distinctive feature of the method of nonlinear control systems design considered below is the use of the nonlinear plants models represented in a quasilinear form. This form of the nonlinear differential equations exists, if nonlinearities in their right parts are differentiated across all arguments. The quasilinear model of the controlled plant allows reducing the design problem to the solution of an algebraic equations system, which has the unique solution if the plant is controlled according to the controllability condition provided in the article. This condition is similar to the controllability condition of the Kalman’s criterion. Procedure of the nonlinear control systems design on a basis of the plant’s quasilinear models is very simple. Practically, it is close to the known polynomial method of the linear control systems design. The equations of the nonlinear systems designed with application of the plant’s quasilinear models also can be represented in the quasilinear form.
 The basic result of this article is the proof of the theorem and the corollary from it about conditions of the asymptotical stability at whole of the equilibrium point of the nonlinear control systems designed on a basis of the plant’s quasilinear models. For the proof of the theorem and consequence, the properties of simple matrixes and known theorems of stability of the indignant systems of the differential equations are used. A way of the stability research of the equilibrium point of the quasilinear control systems based on the proved theorem is illustrated by numerical examples. Computer simulation of these systems verifies correctness of the hypoyhesis of the proved theorem.
 Obtained results allow applying the method of nonlinear systems design on a basis of the quasilinear models for creation of various control systems for plants in power, aviation, space, robotechnical and other industries.

A practical challenge-response authentication mechanism for a Programmable Logic Controller control system with one-time password in nuclear power plants

Abstract Instrumentation and Control (I&C) systems of nuclear power plants (NPPs) have been continuously digitalized. These systems have a critical role in the operation of nuclear facilities by functioning as the brain of NPPs. In recent years, as cyber security threats to NPP systems have increased, regulatory and policy-related organizations around the world, including the International Atomic Energy Agency (IAEA), Nuclear Regulatory Commission (NRC) and Korea Institute of Nuclear Nonproliferation and Control (KINAC), have emphasized the importance of nuclear cyber security by publishing cyber security guidelines and recommending cyber security requirements for NPP facilities. As described in NRC Regulatory Guide (Reg) 5.71 and KINAC RS015, challenge response authentication should be applied to the critical digital I&C system of NPPs to satisfy the cyber security requirements. There have been no cases in which the most robust response authentication technology like challenge response has been developed and applied to nuclear I&C systems. This paper presents a challenge response authentication mechanism for a Programmable Logic Controller (PLC) system used as a control system in the safety system of the Advanced Power Reactor (APR) 1400 NPP.

Plantwide control systems design and evaluation applied to biodiesel production

Chemical processes have complex dynamic behaviors due to the presence of recycle streams, heat integration and several unit operations being interconnected, leading to interaction problems among variables and difficulties in completing an effective process control. Plantwide control methodologies aim to establish control systems for entire chemical plants; however, it is possible to obtain different control solutions. This work proposes that the evaluation of different plantwide control structures for a specific process could be carried out using key performance indicators (KPIs) to determine which control method best meets the industry strategic goals. In order to evaluate the proposed approach a typical biodiesel process model was implemented in Aspen Plus Dynamics; the selected KPIs were the dynamic disturbance sensitivity and an economic indicator that represents the variation of the ratio between the product’s selling price and the raw material cost over time. It was observed that both KPIs allowed a view of the plantwide control system performance and aided in choosing a set of designed controllers. However, the economic indicator enables one to choose a set of designed controllers that reduce the variability of the economic indicator by around 74% while providing a slight increase in the indicator mean value.

Russian stationary vibration control and mechanical displacement systems for electric power pumps of thermal power plants

The article discusses the possibility of using Russian stationary vibration and mechanical quantities control systems for electric power boilers of thermal power plants, in particular, the implementation of automated control of absolute vibration bearing, axial shear and speed with the requirements of regulatory documents. A review and analysis of the market of stationary systems for monitoring vibration and mechanical quantities, their technical and metrological characteristics was carried out. The possibility of integrating Russian stationary systems for monitoring vibration and mechanical quantities into automated process control systems of thermal power plants, their application in various subsystems, including the subsystem of technological protection and safety locks, is considered. An assessment was made of compliance with regulatory documents governing the construction of such systems, taking into account the requirements of supervisory authorities.

Development of Real-Time Controller-Based Data Acquisition System for Indian Test Facility of ITER DNB

The Indian test facility (INTF) is a negative hydrogen ion-based 100-kV, 60-A, 5-Hz modulated NBI system having 3-s ON/20-s OFF duty cycle. Prime objective of the facility is to characterize ITER diagnostic neutral beam (DNB) with full specifications, prior to shipment and installation in ITER. The automated and safe operation of the system will require a reliable and rugged instrumentation and control system which provide control, data acquisition (DAQ), safety, and interlock functions, referred as INTF-DACS. The INTF-DACS has been designed based on the ITER CODAC architecture and ITER- plant control design handbook (PCDH) guidelines with the aim of developing the technical understanding of CODAC framework to be utilized for development of plant system instrumentation and control for DNB. Presently, the development work has been initiated for both the control system and DAQ system of INTF DACS. The INTF DAQ system has to perform functions related to acquiring, monitoring, timing synchronization, and archiving of the signals. It also has to interface with the control system of INTF to ensure proper operations. The DAQ system is designed for acquiring over 700 signals for 14 plant systems. The development of this whole system is done in NI LabVIEW using NI real-time PXIe. The PXIe platform with RTOS performs acquisition of signals at sampling rate of up to 10 KS/s. One of the main challenges is to develop the DAQ system to support multichannel triggered-based acquisition and monitoring for pulse durations up to 3600 s. The host layer is a distributed processing system consisting of two hosts and database system. To ensure timing synchronization, a dedicated timing network is included based on IEEE 1588 protocol with help of PXI timing cards. This helps in providing a timing reference to other future systems. For archiving data, MySQL-based data server is integrated for storing data for each experimental shot continuously which can be utilized later for query based data retrieval. In this paper, the development strategy and test results are discussed in order to develop the DAQ system for INTF including the development of interfaces with other components of DACS and experiences obtained, which can be utilized to develop similar DAQ systems of large scale. The novel methods developed for monitoring signals and file size reduction are also discussed.

ITER upper visible/infrared wide angle viewing system: I&C design and prototyping status

The ITER Upper Visible/Infrared Wide Angle Viewing System is a key diagnostic system for divertor surface temperature monitoring and heat load calculation during plasma operation. This system will be installed after the first plasma phase in five upper ports with front-end optics under vacuum, relay optics in the interspace, back-end optics and sensors in the port-cells, and data acquisition and processing units in the Diagnostic building. The system is currently in the Preliminary Design phase which includes some prototyping activities. This paper describes the current design status of the plant system Instrumentation and Control (I&C) comprising camera pre-selection, hardware, and software architecture for camera data acquisition and image processing. The proposed design has been elaborated by following the ITER CODAC methodology for Plant System I&C design. On-going prototyping activities addressing identified R&D challenges such as camera high throughput data acquisition and real-time image processing are also presented.

CPN simulation-based test case generation from controlled natural-language requirements

We propose a test generation strategy from natural language (NL) requirements via translation into Coloured Petri Nets (CPN), an extension of Petri Nets that supports model structuring and provides a mature theory and powerful tool support. This approach extends our previous work on the NAT2TEST framework, which involves syntactic and semantic analyses of NL requirements and the generation of Data-Flow Reactive Systems (DFRS) as an intermediate representation, from which target formal models can be obtained for the purpose of test case generation. Our contributions include automating a systematic translation of DFRSs into CPN models, an extension to deal with time aspects, besides an empirical analysis of the CPN-based test generation strategy. The analyses considered examples both from the literature (a vending machine and a nuclear power plant control system), and from the aerospace and the automotive domain (a priority command control system and a turn indicator control system, respectively). We analysed performance and the ability to detect defects generated via mutation. The results provide evidence that the contribution proposed here is more efficient, besides being able to detect at least as many defects as our previous efforts. • Test case generation for timed reactive systems from natural-language requirements. • Coloured Petri Nets (CPN) are used as a hidden formalism in the generation process. • Generation of CPN models is systematised with the aid of the Spoofax framework. • Test generation is performed via simulation of CPN models. • The strategy is evaluated (performance and test strength) using four applications.

Automatic generation control for the flexible operation of multimodular high temperature gas-cooled reactor plants

To balance the intermittent renewable energy (IRE) and to realize its deep penetration, it is necessary for nuclear power plants (NPPs) to operate with enough flexibility. This necessity leads to the concerned questions such as which types of nuclear reactors are suitable for flexible operation and how to realize the operational flexibility of NPPs. In this paper, based on literature review and related analysis, it is shown that the modular high temperature gas-cooled reactor (MHTGR) is suitable for balancing IRE because of the advanced features such as robust fuel elements, online fuel handling, low power density and full-power-range temperature negative feedback effect. Due to the low power density, the power rating of a single MHTGR is lower than those large commercial pressurized water reactors (PWRs). To balance IRE by MHTGRs in a scalable manner, it is recommended to develop NPPs with high rated power based on multimodular scheme, i.e. multiple MHTGR-based nuclear steam supply system (NSSS) modules providing superheated steam for a common turbine. Further, to realize the flexible operation of MHTGR for deep IRE penetration, the automatic generation control (AGC) of multimodular MHTGR plants should be developed. In this paper, two AGC methods including both the adaptive AGC and extended-state-observer (ESO) based AGC are proposed, where the former one has a simple proportional-integral (PI) structure, and the latter one has an additional feedforward compensating action determined by the ESO. The corresponding control system of multimodular MHTGR plants is also designed, which is composed of the units of NSSS control, multimodular coordination control, turbine speed governor (TSG) and AGC. The AGC methods as well as the plant control system design with AGC function are then applied to two modular MHTGR plant HTR-PM. Numerical simulation results show that the newly-built multimodular control system can well stabilize the grid frequency by properly performing the power-level maneuver and maintenance of NSSS modules, and also show that the ESO-based AGC has a better frequency stabilization performance than the adaptive AGC does.

Design and Operational Strategy Research for Temperature Control Systems of Isothermal Compressed Air Energy Storage Power Plants

Energy storage technology is critical for intelligent power grids. It has great significance for the large-scale integration of new energy sources into the power grid and the transition of the energy structure. Based on the existing technology of isothermal compressed air energy storage, this paper presents a design scheme of isothermal compressed air energy storage power station, which uses liquid to compress air, hydraulic piston to transfer potential energy, hydraulic turbine to generate electricity at constant pressure, and liquid occupancy to store the gas at constant pressure. Then the technical features and control strategies of its internal temperature control subsystem are studied, and the mathematical model is constructed. A hierarchical relay operation is put forward to address the actual construction and operational requirements of compressed air energy storage power plants. Finally, through physical platform experiments and MATLAB simulation, the feasibility of the design is validated.

REQUIREMENT ANALYSIS OF COMPUTER-BASED INSTRUMENTATION AND CONTROL SYSTEM FOR REAKTOR DAYA EKSPERIMENTAL

Developing and licensing of digital Instrumentation and control (I&C) system for nuclear power plant (NPP) are challenging especially for the new construction since digital technology are composite with a very high complexity of many integrated systems. National Nuclear Energy Agency of Indonesia (BATAN), who design Reaktor Daya Eksperimental (RDE), should prepare the documents to meet the licensing requirements of national regulator in this case Nuclear Energy Regulatory Agency of Indonesia (BAPETEN). BAPETEN’s chairman regulation No.6 year of 2012 is the first national requirement which state requirements related to design of computer-based system concerning on safety of power reactor that should be followed. Since BAPETEN only denotes requirements without state which code and standards to be used, therefore BATAN can add references from International Nuclear Energy Agency (IAEA) guidelines. In this paper, requirement document traceability is developed to determine which code and standards should be used to verify and validate the I&C computer-based system of RDE. The hierarchy of regulatory and utility requirements are developed to guide the design basis documentation. Developing requirements analysis of computer-based I&C system RDE are completed after determining the design requirements from the utility and regulatory requirements. This methodology will help the design engineers to follow the utility requirements by concerning to the production, and follow the regulatory requirements concerning the safety aspect.Keywords: Computer-based system, I&C System, Requirements analysis, Licensing, RDE

Design of safety critical and control systems of Nuclear Power Plants using Petri nets

Abstract Non-functional requirements plays a critical role in designing variety of applications domain ranges from safety-critical systems to simple gaming applications. Performance is one of the crucial non-functional requirement, especially in control and safety systems, that validates the design. System risk can be quantified as a product of probability of system failure and severity of its impact. In this paper, we devise a technique to do the performance analysis of safety critical and control systems and to estimate performance based risk factor. The technique elaborates Petri nets to estimate performability to ensure system dependability requirements. We illustrate the technique on a case study of Nuclear Power Plant system. The technique has been validated on 17 safety critical and control systems of Nuclear Power Plant.

Choosing and Evaluating Fabrication Processes by Means of a Computer-Aided Innovation Support System Based on the Morphological Approach

This article considers application of the advanced morphological approach as a computer-aided innovation (CAI) support system for choosing and evaluating new technology solutions. The main goal of the approach is to expand the range of potential variants and to clusterize and efficiently choose a decision space for synthesis for the purpose of increasing the feasibility of innovative solutions in the design phase. The suggested technique relies on the cluster analysis, theory of sets, and making up a set of rules to maximize the potential level of developed technologies. The application of the approach is shown by several examples. The analysis and choice of technology solutions, fabrication processes, and control systems for microarc oxidation plants and PU foam milling processes are considered.

Transient Processes in Air Separation Plants

A modern air separation plant control system must solve a host of problems, including variation in conditions of plant operation with full guarantee of its automatic flow. The procedure of gearing the plant from one operation mode to another is based on gradual change of control action and collection of desired products without impairment of their quality below the allowable level. To accomplish this task, it is essential to determine the values of the key process parameters for various air separation plant operation conditions and the maximally allowable control action variation rate. Based on the investigation results and comparative analysis of the values of the key process parameters of optimized static-state regimes in UniSim Design environment and actual indicators with a real plant, we found insignificant deviation of the calculated parameters from the actual values during the plant operation. It was concluded that the results of air separation process modeling in UniSim Design environment or the magnitudes of control actions derived by equations of material and heat balances of the plant can be used, in a first approximation, in plant operation mode change algorithm.

Современное состояние и перспективы развития систем автоматического управления и регулирования теплоэнергетических установок

Современное состояние и перспективы развития систем автоматического управления и регулирования теплоэнергетических установок

Survey on fuzzy logic methods in control systems of electromechanical plants

The paper reviews control algorithms of electromechanical systems using the theory of fuzzy logic, describes basic principles of synthesis of these systems, discusses methods for analyzing their stability based on fuzzy Lyapunov functions. These algorithms are most often implemented in the form of various controllers, which application is justified in the systems with unknown mathematical model, or not determined, or strictly nonlinear, with nonlinear disturbances in their structure or in the external forces. We describe the basic methods of inference used in the design of various types of fuzzy logic controllers proposed by Zadeh, Mamdani, Takagi, Sugeno, and Mendel. A typical structural scheme of such controllers is given. The considered applications of these controllers in the control of various technical plants give the possibility to classify them according to various criteria: topologies of structures, inference mechanism, methods of defuzzification, types of membership functions. We review methods for adjustment of such controllers by genetic algorithms and neural networks with a description of the most commonly used criteria for optimality estimation. It is shown that the use of an expert approach based on fuzzy logic is applicable both in control of various coordinates of information subsystems of robotic complexes, and in control of the power switches of their energy subsystems. In the review of publications, the main attention was given to sources containing comparison with traditional approaches to control, as well as sources in which theoretical studies are supported by experiments involving various electromechanical plants. The paper may be useful to specialists and researchers in the field of control of various technical devices.

Dynamical modeling and simulation analysis of a nuclear desalination plant based on the MED-TVC process

Nuclear fission reaction is a clean energy source that can provide thermal power to desalination processes for producing potable water. Due to the inherent safety features of the integral pressurized water reactor (iPWRs) and economic competitiveness of the multi-effect-desalination and thermal-vapor-compression (MED-TVC) process, it is reasonable to interconnect the iPWR with MED-TVC process to develop nuclear desalination plants (NDPs). Dynamic modeling is important for both the design and optimization of the control systems for nuclear desalination plants. In this paper, based on the balance of mass, momentum, energy and salt, a lumped-parameter dynamic model for the NDP composed of an iPWR named NHR-200II and the MED-TVC process is given for the plant control design, which is further deployed as a program on Matlab/Simulink platform. For the modeling verification, the steady points of some key process variables are shown with comparison to the design data, and the open-loop responses under the stepping of both the input seawater flowrate and TVC throat cross-section area are given, which not only show accuracy of this model but also illustrate the coupling between the nuclear steam supply system (NSSS) and MED-TVC modules. Then, a plant control strategy of the NDP based upon NHR-200II reactor and MED-TVC module is newly proposed. Based on the dynamic model, the control verification is finally performed, and the closed-loop responses in the cases of both power maneuvering and MED-TVC module bypassing show the feasibility and satisfactory performance of this control design.