Flexible Control Structure Research Articles

Full cycle on-line autonomous reconfiguration of MIMO control system based on REGA pairing principle for heat exchanger networks

This study presents a novel autonomous reconfiguration strategy to achieve full cycle optimal control of the heat exchanger networks. The proposed method aims to select the optimal control structure online to solve the problem of slow time-varying process transition caused by the inevitable fouling accumulation. An auxiliary variable is introduced to increase the degree of control freedom, and a flexible control structure is studied to provide appropriate pairings dynamically between variables. Subsequently, the nonparametric Relative Energy Gain Array (REGA) is considered to form the switching mechanism that determines the switching instants and variable pairing modes between control loops. Furthermore, the online optimization of switching regions ensures the optimal control performance. Finally, one typical experiment for the heat exchanger network in crude distillation unit was conducted and the results illustrated the effectiveness of the proposed control method. Compared with the conventional control system, the available service time is extended by nearly 18 months, and there is still room for further adjustment.

Experimental model validation and predictive control strategy for an industrial fire-tube boiler

This paper presents a flexible control structure for fire-tube boilers based on a suitable integration of the typical decentralized PI control structure and model predictive control technique. First, a dynamic nonlinear reference model of the fire-tube boilers is developed combining models available in the technical literature, based on first principle laws. The overall system model is considered as a gray-box model, and it has been validated with real data. Then, a suitable control-oriented model is derived out of the nonlinear reference model, in order to design a hybrid cascade MPC-PI control structure capable of guaranteeing stability, improving performances and enforcing real-time constraints. The flexibility of such a structure can be exploited to impose different types of functional behavior to the boiler itself, from the performance-related ones to the efficiency increase ones. While the reference non-linear model is large and detailed, the control-oriented one is simplified so that a few process parameters are identified to reduce dramatically the implementation in the MPC controller hardware and software framework. A sensitivity analysis with respect to these process parameters highlights the robustness and easy implementation of such a strategy. Two MPC configurations have been developed and tested in simulation over the validated boiler model. Then, a customized algorithm has been developed to understand a massive quantization phenomenon on the boiler pressure measurement. Finally, a test session conducted on a real fire-tube boiler quantifies the performance benefits of one configuration of the MPC-PI control structure with respect to the PI control. • Tuning of a dynamic nonlinear reference model of the fire-tube boilers with real data. • A hybrid cascade MPC-decentralized PID control structure, easly tunable. • Sensitivity analysis to test the robustness and easy implementation of such a control strategy. • A customized algorithm to reject a massive quantization on the boiler pressure measurement. • Implementation of the optimal control strategy and test session on a real fire-tube boiler.

NATO burden-sharing: past, present, future

ABSTRACT How can NATO upgrade its understanding of (and metrics for) fair burden-sharing? Alliance burden-sharing is a lasting concern for the North Atlantic Treaty Organization (NATO) and will remain a focal point of the NATO 2022 Strategic Concept. Public discussions of NATO burden-sharing and the 2014 Defense Investment Pledge overemphasize defense expenditure and fail to account for alternative frameworks for understanding alliance burden-sharing and specifically, NATO’s optimal burden-share distribution. The U.S. Military Academy’s February 2022 NATO Strategic Concept Seminar featured a panel on burden-sharing frameworks and metrics. In this article, we present the main ideas and arguments, placed within the existing literature on alliance burden-sharing. We argue that, in the long-run, NATO can develop more fair, effective, and efficient burden-sharing arrangements by encouraging weapons and capability specialization, increasing inexpensive but influential operations such as advisory missions, and adapting flexible command and control structures when partnering with non-NATO actors on future battlefields. We argue that, in the short-run, NATO can refine the Defense Investment Pledge with a balanced focus on Cash, Capabilities, and Contributions while also extending the deadline for complete compliance with existing expenditure benchmarks until 2030.

Adaptive Fuzzy Fractional Order Global Sliding Mode Tracking Control Algorithm for Particleboard Glue System

In this paper, a novel flow tracking control scheme for particleboard glue system with complex disturbance and unmeasurable system state is investigated. The method is based on hyperbolic tangent extended state observer and adaptive fuzzy fractional order global sliding mode control with exponential reaching law. The novel compound control scheme has the following advantages: Firstly, the extended state observer with hyperbolic tangent function can improve the estimation ability for the system state and complex disturbance without detailed knowledge of the controlled plant and disturbance model. Secondly, the global sliding mode control method based on fractional calculus can improve the response speed and robustness of the system, and provide a more flexible controller structure than the traditional sliding mode controller. Thirdly, the adaptive fuzzy controller is introduced to approximate the sliding mode switching term, so as to reduce the chattering phenomenon of the system. In addition, the convergence of the proposed observer and asymptotic stability of the control system are verified based on strict Lyapunov analysis. Finally, the numerical simulation results show the effectiveness of the proposed compound control scheme for particleboard glue system.

Integrated water resource management to address the growing demand for food and water in South Asia*

AbstractWith the increasing population and accelerated urbanization, demands for water are rising for different sectors around the world, including in South Asia. Integrated water resource management (IWRM) offers a promising potential to address multifaceted water demands. This study therefore aimed to address this issue by (i) reviewing key issues related to water, land, and food in South Asian countries, (ii) exploring the prevalent irrigation management strategies in those countries, and (iii) examining the IWRM situation based on a Nepalese case study, and it proposes some options to support effective implementation of IWRM.South Asia, the home to 24% of the world's population with only 15% and 7% of the world's arable and permanent crop land and water resources, respectively, is the worst‐affected region in the world from undernourishment. Surface irrigation is the dominant irrigation application method in the region, which incurs high water losses due to the lack of flexible water control structures in canal networks. The Nepalese case study revealed a lack of clear institutional arrangements to implement IWRM and disparate and conflicting views about IWRM. Creation and strengthening of basin‐level water user organizations, technological improvements, and awareness‐raising activities are some potential ways forward to implement IWRM.

Trajectory tracking control for electro-optical tracking system based on fractional-order sliding mode controller with super-twisting extended state observer

This paper investigates a trajectory tracking control scheme for electro-optical tracking systems subject to friction and other nonlinear disturbances. The proposed approach is based on a super-twisting extended state observer (ESO) and a fractional-order nonsingular terminal sliding mode (FONTSM) with a switching-type reaching law. The novel hybrid control scheme exhibits the following advantageous characteristics. First, the extended state observer injected with a super-twisting algorithm is capable of simultaneously estimating the friction and other nonlinear disturbances without detailed knowledge of the precise friction and disturbance models. Second, the FONTSM surface enhances the control accuracy and robustness, and provides a more flexible controller structure than its integer counterpart. Third, a novel switching-type reaching law is utilized to achieve fast response, constraining chattering in the system. Additionally, the finite-time convergence of the adopted ESO and the finite-time stability of the control system are demonstrated based on the rigorous Lyapunov criteria. Finally, the effectiveness of the proposed hybrid control scheme is demonstrated for an electro-optical tracking system via trajectory tracking experiments.

Flexible Control Structure for Enhancement of Scalability in DC Microgrids

In this article, a new control structure is proposed to improve the scalability of dc microgrids. Because conventional control structures require implementation of higher control level, subsystems that do not include them cannot be added in a microgrid. However, there are many subsystems in the field that do not support higher control level, which hinders microgrid scalability. For such subsystems to perform these functions, their local controller should be modified, which requires a lot of time and economic effort. In this article, by adding a new controller that performs higher control level without changing the local controller of subsystems, a structure to expand the scalability of a dc microgrid is proposed. The proposed flexible control structure consists of a local controller of subsystems, a flexible controller that performs higher control level, and microgrid central controller. A new communication network is required between local controller and flexible controller. However, due to a communication delay, the overall system stability is reduced. Therefore, problems related to the additional communication network were analyzed and a compensator was designed to overcome these issues. Through the flexible control structure, a subsystem that does not support higher control level can be added to dc microgrid.

Inline detection of Denial of Service Attacks in Software Defined Networking using the Hotelling Chart

Software Defined Network (SDN) has become the true trend of the IT service model offering a cost-effective and scalable processing solution. Although central control is the major asset of the SDN, it is also a single point of failure if it is made inaccessible by a distributed denial of service (DDoS) attack. Despite the number of existing traditional detection solutions, DDoS attacks continue to increase in frequency, volume and severity. This paper provides an analysis of the problem by examining the impact on security, particularly for distributed denial of service (DDoS) attacks that is still a threat to SDN software-defined networks and suggests the proposal and implementation of a DDoS attack detection algorithm. Based on an architecture that integrates highly programmable network monitoring and a flexible control structure to enable fast and specific attack detection. To cope with the new architecture, we propose an attack detection system based on a statistical model that can address the problem of flooding attack and bandwidth attack. The simulation results show that our architecture can effectively address the security challenges posed by the new network paradigm and our attack detection system can effectively signal various attacks using real-world network traffic.

A Modified RBF Neuro-Sliding Mode Control Technique for a Grid Connected PMSG Based Variable Speed Wind Energy Conversion System

A modified control scheme based on the combination of online trained neural network and sliding mode techniques is proposed to enhance maximum power extraction for a grid connected permanent magnet synchronous generator (PMSG) wind turbine system. The proposed control method does not need the knowledge of the uncertainty bounds nor the exact model of the nonlinear system. Since the neural network is trained online, the time to estimate good weights can affect the dynamic performance of the process during the startup phase. Therefore an appropriate way to smoothly and explicitly accelerate the neural network rate of convergence during the startup phase is proposed. Furthermore, a flexible grid side voltage source converter control structure which can handle both grid connected and standalone modes based on conventional proportional integral (PI) control method is presented. Simulations are done in Matlab/Simulink environment to verify the effectiveness and assess the performance of the proposed controller. The results analysis shows the superiority of the proposed RBF neuro-sliding mode controller compared to a nonlinear controller based on sliding mode control method when the system undergoes parameter uncertainties.

A Sequential Integration between Optimal Flexible Heat Exchanger Network Synthesis and Control Structure Design

In this work, the optimal synthesis and control structure design (CSD) problems for flexible heat exchanger networks (HENs) are integrated into a new sequential methodology. The proposed approach r...

Bed Morphology around Various Solid and Flexible Grade Control Structures in an Unstable Gravel-Bed River

Flexible grade control structures (GCSs) are increasingly popular alternative countermeasures consisting of conventional solid structures for protecting riverbeds from erosion. Among this structure typology, tetrahedron framed permeable weirs (TFPW) were proposed to stabilize riverbeds and protect cross-river structures. The bed morphology as well as the interactions among the structures, water flow and bed features have not been systematically analyzed. Therefore, based on the field data collected in the Jianjiang River, a series of physical model experiments were carried out in this study to investigate the river morphology in unstable gravel-bed rivers under five different structural conditions, including no GCSs, solid bed sills and flexible TFPW with three different layout types. Data on bedform features, topography changes and the volume of erosion or deposition were collected and analyzed. The results indicated that dramatic general erosion and bed armoring would occur without any protection. The bed would be protected from upstream erosion with bed sills, but, at the same time, in addition to general erosion and bed armoring downstream of the structures, deep local scour might pose a serious threat to structural safety. TFPW had good protective effects on riverbeds by preventing the bed from erosion and even inducing sediment deposition both upstream and downstream from the structures. Because the flexible structures have advantages in ecology, structural stability and construction, TFPW were suitable and optimal for riverbed stabilization in unstable gravel-bed rivers.

Efficient pump and meter-out control for electrohydraulic system with time-varying negative load

In hydraulic systems under negative loads, counterbalance valves are widely employed, which introduce instability and sizable energy consumption. This article focuses on the electrohydraulic system with meter-out orifice and variable pump, which allows flexible control structure. The target is to reduce inlet pressure level as well as diminish oscillation caused by time-varying loads. An extended load observer is constructed to estimate the external load. Accordingly, a robust back-stepping controller with integral part and disturbance compensation is proposed to regulate the meter-out orifice, achieving velocity-oriented control. Also, a model-based pressure-oriented controller is developed to determine pump displacement. The target is set to 3 bar in this work, while the pressure losses in conventional systems are more than 12 bar. The stabilities of these two independent controllers are both proved by Lyapunov theory. Experiments focusing on energy consumption, load compensation, and velocity tracking are carried out verifying the controller effectiveness. Discussions of results illustrate that the whole proposed controller succeeds in velocity tracking and reducing energy consumption in the presence of time-varying negative load.

OpCloudSec: Open cloud software defined wireless network security for the Internet of Things

Cutting-edge cloud frameworks will require a paradigm shift in regards to how they are built and managed. Traditional management and control platforms face significant challenges in terms of security, reliability, and flexibility that these cutting-edge frameworks must deal with. On the other hand, Distributed Denial of Service (DDoS) attacks have become a weapon of choice for cyber-terrorists, cyber-extortionists, and hackers. Recently, the simplicity of programmability in Software-Defined Networking (SDN) makes it a good platform for the implementation of various initiatives that includes decentralized network management, dynamic topology changes, and application deployment in a multi-tenant data center environment. Motivated by the capabilities of SDN, we are proposing a mitigation architecture for security attacks that incorporates a highly programmable monitoring network so as to make it possible to identify attacks. It has a flexible control structure to quickly define the reaction of attacks and particular side, and we show how SDN can be used as a key application in the cloud IoT. We evaluated the performance of our proposed architecture and compared it with the existing models to obtain various performance measures. The results of our evaluation show that our OpCloudSec architecture model can efficiently and effectively meet the security challenges created by the new network paradigm.

Energy efficiency technologies in cement and steel industry

In this paper, Advanced Process Control strategies aimed at energy efficiency achievement and improvement in cement and steel industry are proposed. A flexible and smart control structure constituted by several functional modules and blocks has been developed. The designed control strategy is based on Model Predictive Control techniques, formulated on linear models. Two industrial control solutions have been developed, oriented to energy efficiency and process control improvement in cement industry clinker rotary kilns (clinker production phase) and in steel industry billets reheating furnaces. Tailored customization procedures for the design of ad hoc control systems have been executed, based on the specific needs and specifications of the analysed processes. The installation of the developed controllers on cement and steel plants produced significant benefits in terms of process control which resulted in working closer to the imposed operating limits. With respect to the previous control systems, based on local controllers and/or operators manual conduction, more profitable configurations of the crucial process variables have been provided.

DDoS attack protection in the era of cloud computing and Software-Defined Networking

Cloud computing has become the real trend of enterprise IT service model that offers cost-effective and scalable processing. Meanwhile, Software-Defined Networking (SDN) is gaining popularity in enterprise networks for flexibility in network management service and reduced operational cost. There seems a trend for the two technologies to go hand-in-hand in providing an enterprise’s IT services. However, the new challenges brought by the marriage of cloud computing and SDN, particularly the implications on enterprise network security, have not been well understood. This paper sets to address this important problem.We start by examining the security impact, in particular, the impact on DDoS attack defense mechanisms, in an enterprise network where both technologies are adopted. We find that SDN technology can actually help enterprises to defend against DDoS attacks if the defense architecture is designed properly. To that end, we propose a DDoS attack mitigation architecture that integrates a highly programmable network monitoring to enable attack detection and a flexible control structure to allow fast and specific attack reaction. To cope with the new architecture, we propose a graphic model based attack detection system that can deal with the dataset shift problem. The simulation results show that our architecture can effectively and efficiently address the security challenges brought by the new network paradigm and our attack detection system can effectively report various attacks using real-world network traffic.

Comparative Performance Analysis of Coordinated Model Predictive Control Schemes in the Presence of Model–Plant Mismatch

Large-scale systems are formed by the interconnection of several subsystems, whose different spatial and temporal characteristics make them significantly heterogeneous. The optimal management of such systems must generally deal not only with issues related to large dimensionality and strong nonlinearity, but also with the presence of several interactions between the subsystems, which have a significant influence on the local control decisions and the overall system optimality. For such large-scale systems, model predictive control (MPC) is an attractive control strategy and can be implemented in centralized or decentralized configurations. It has been shown that, to achieve a flexible and reliable control structure with optimum overall system performance, individual decentralized controllers have to be coordinated and driven toward the performance of a centralized controller. In this work, three coordination strategies that have been reported in the literature, viz., communication based coordination, cooperation based coordination, and price driven coordination, are evaluated for controlling multivariable processes. These three strategies have been evaluated on a benchmark chemical engineering system and on a quadruple tank system (via simulations), on the basis of their robustness, stability, and performance in comparison to that of a centralized MPC implementation. The ability to deal with a variety of model uncertainties and the coordination between the controllers within and across a hierarchy are some important aspects that have been investigated.

Application of a thermally coupled distillation column with separated main columns to gas concentration process

A modified fully thermally coupled distillation column (FTCDC) for operability improvement is utilized in a gas concentration process. The column consists of a prefractionator and two separated main columns having high distillation efficiency and flexible control structure. The operability of the proposed column is evaluated by examining the open-loop dynamic responses of step input variations with the HYSYS simulation. The simulation result indicates that the modified system can give better control than the original FTCDC. The energy saving and reduction of con- struction cost are discussed, and the ease of vapor flow manipulation and the elimination of a compressor in the vapor transfer are also evaluated as possible improvements.

2202 人に優しい自律分散型生産システムに関する研究 : 作業者の希望を考慮したリアルタイムスケジューリング(OS2-2 スケジューリングII)

Recently, new distributed architectures of manufacturing systems are proposed, aiming at realizing more flexible control structures of the manufacturing systems. However, the human operators have not yet been discussed for the autonomous components of the distributed manufacturing systems. A real-time scheduling method is proposed, in this research, to select suitable combinations of the human operators, the resources and the jobs for the manufacturing processes. The proposed scheduling method consists of following three steps. In the first step, the human operators select their favorite manufacturing processes which they will carry out in the next time period, based on their preferences. In the second step, the machine tools and the jobs select suitable combinations for the next machining processes. In the third step, the automated guided vehicles and the jobs select suitable combinations for the next transportation processes.

Flexible Controller Design and Its Application for Concurrent Execution of Buffer Centric Dataflows

This paper presents a flexible controller structure for concurrent processing of memory centric coarse grain data flows. We propose a design flow based on block level pipelining where concurrency among processing blocks is fully maintained. The controller is dynamically reconfigurable to support dynamic data-flow structure changes by localizing control signals. The proposed control design method isolates controllers and processing logics such that system integration is simplified while controllers are locally configured from orthogonal global information. The controller also supports interfacing with external processors for asynchronous processing. The controller for heterogeneous processing blocks is synthesized and verified using Verilog and SystemC on FPGA. We present an example demonstrating the effectiveness of the controllers where dynamic reconfiguration of the execution is feasible.

A model-free control structure for the on-line tuning of the semi-active suspension of a passenger car

Comfort and road handling of a passenger car can be improved by replacing its passive suspension by a controlled semi-active suspension. The selection of an appropriate control structure is crucial, since it determines the complexity of the control design and parameter tuning process. This paper presents a flexible and transparent model-free control structure based on (1) physical insights in the car and semi-active suspension dynamics used to linearise and decouple the system, and (2) decentralised linear feedback. The resulting controller can be tuned on-line intuitively using a limited number of physically interpretable parameters. The simplicity of the control structure and the absence of any model of either the car or the shock absorber yields that the code of the controller can run on a low-cost DSP with a minimum amount of memory. The evaluation of experienced test-pilots states that the car with tuned controller behaves naturally, yields comfortable ride on a wide variety of calibrated evaluation tracks and yet is well controlled during all handling manoeuvres.