Hierarchical Control Concept Research Articles

On the Computation of Hierarchical Control results for One-Dimensional Transmission Line

In this paper, motivated by a physics problem, we investigate some numerical and computational aspects for the problem of hierarchical controllability in a one-dimensional wave equation in domains with a moving boundary. Some controls act in part of the boundary and define a strategy of equilibrium between them, considering a leader control and a follower. Thus, we introduced the concept of hierarchical control to solve the problem and mapped the Stackelberg Strategy between these controls. A total discretization of the problem is presented for a numerical evaluation in spaces of finite dimension, an algorithm for evaluation of the problem is presented as the combination of finite element method (FEM) and finite difference method (FDM). The algorithm efficiency and computational results are illustrated for some experiments using the softwares Freefem++ and MatLab.

Design and implementation of the floor tiling robot control system based on multi-motion unit structure and hierarchical control

The floor tiling is a hard work, and a high level of skill is also necessary for the operators. Therefore, the current global floor tiling construction costs continue to increase. The use of robots to replace manual operations is becoming more urgent. Robotic floor tiling can reduce the work intensity of workers while improving the efficiency and the quality. This paper proposes a control system scheme for a floor tiling robot. Based on the characteristics of the multi-motion unit structure of the robot and the design concept of hierarchical control, the control system was divided into the user layer, the system control layer, the intermediate drive layer and the hardware execution layer. The system had clear functions and strong reusability. The user layer played a role of human-computer interaction which received the user’s instructions. The system control layer was the brain of the robot, which was mainly responsible for the coordinated control of all the motion units during the floor tiling process. The middle driver layer provided the device controllers for all dedicated hardware devices, realized recognition of system control layer instructions and took the hardware execution layer devices to work. The hardware execution layer mainly executed the actions in the process of the floor tiling. The test results show that the control system can realize stable control for the floor tiling operation, and the system is stable and reliable. The research results on this study would provide a reference for the control system design of other construction robots or special equipment robots.

Hierarchical nonlinear optimization-based controller of a continuous strip annealing furnace

Continuous strip annealing furnaces are complex multi-input multi-output nonlinear distributed-parameter systems. They are used in industry for heat treatment of steel strips. The product portfolio and different materials to be heat-treated is steadily increasing and the demands on high throughput, minimum energy consumption, and minimum waste have gained importance over the last years. Designing a furnace control concept that ensures accurate temperature tracking under consideration of all input and state constraints in transient operations is a challenging task, in particular in view of the large thermal inertia of the furnace compared to the strip. The control problem at hand becomes even more complicated because the burners in the different heating zones of the considered furnace can be individually switched on and off. In this paper, a real-time capable optimization-based hierarchical control concept is developed, which consists of a static optimization for the selection of an operating point for each strip, a trajectory generator for the strip velocity, a dynamic optimization routine using a long prediction horizon to plan reference trajectories for the strip temperature as well as switching times for heating zones, and a nonlinear model predictive controller with a short prediction horizon for temperature tracking. The mass flows of fuel and the strip velocity are the basic control inputs. The underlying optimization problems are transformed to unconstrained problems and solved by the Gauss–Newton method. The performance of the proposed control concept is demonstrated by an experimentally validated simulation model of a continuous strip annealing furnace at voestalpine Stahl GmbH, Linz, Austria.

Hierarchical and distributed control concept for distribution network congestion management

Congestion management is one of the core enablers of smart distribution systems where distributed energy resources are utilised in network control to enable cost-effective network interconnection of distributed generation (DG) and better utilisation of network assets. The primary aim of congestion management is to prevent voltage violations and network overloading. Congestion management algorithms can also be used to optimise the network state. This study proposes a hierarchical and distributed congestion management concept for future distribution networks having large-scale DG and other controllable resources in MV and LV networks. The control concept aims at operating the network at minimum costs while retaining an acceptable network state. The hierarchy consists of three levels: primary controllers operate based on local measurements, secondary control optimises the set points of the primary controllers in real-time and tertiary control utilises load and production forecasts as its inputs and realises network reconfiguration algorithm and connection to the market. Primary controllers are located at the connection point of the controllable resource, secondary controllers at primary and secondary substations and tertiary control at the control centre. Hence, the control is spatially distributed and operates in different time frames.

Motor control hierarchy in joint action that involves bimanual force production.

The concept of hierarchical motor control has been viewed as a means of progressively decreasing the number of variables manipulated by each higher control level. We tested the hypothesis that turning an individual bimanual force-production task into a joint (two-participant) force-production task would lead to positive correlation between forces produced by the two hands of the individual participant (symmetric strategy) to enable negative correlation between forces produced by two participants (complementary strategy). The present study consisted of individual and joint tasks that involved both unimanual and bimanual conditions. In the joint task, 10 pairs of participants produced periodic isometric forces, such that the sum of forces that they produced matched a target force cycling between 5% and 10% of maximum voluntary contraction at 1 Hz. In the individual task, individuals attempted to match the same target force. In the joint bimanual condition, the two hands of each participant adopted a symmetric strategy of force, whereas the two participants adopted a complementary strategy of force, highlighting that the bimanual action behaved as a low level of a hierarchy, whereas the joint action behaved as an upper level. The complementary force production was greater interpersonally than intrapersonally. However, whereas the coherence was highest at 1 Hz in all conditions, the frequency synchrony was stronger intrapersonally than interpersonally. Moreover, whereas the bimanual action exhibited a smaller error and variability of force than the unimanual action, the joint action exhibited a less-variable interval and force than the individual action.

Management of hybrid energy supply systems in buildings using mixed-integer model predictive control

In this paper a mixed-integer model predictive controller for hybrid energy supply systems in buildings is presented. This approach is based on a hierarchical building control concept where the energy supply level is coupled to the energy consumption level only by the heat load. The supply level is characterized by non-linear dynamics due to a stratified water storage tank and a switched heat pump with minimum on/off times. The mixed-integer model predictive controller optimizes the unit commitment problem at minimum costs while satisfying the consumption level’s predicted heat load. The hybrid system is formulated as a piecewise affine model comprising continuous and discrete system inputs. Moreover, the proposed controller is able to manage the stratified storage tank including switching sequences of the heat pump with respect to energy price forecasts. The effectiveness of this approach is shown by a comparison to a model predictive controller with an a priori fixed operation mode profile, where the heat pump is only operating at night, and discussing the effect of the variation of the stratified storage tank size. The proposed concept is able to flexibly manage all sizes of stratified storage tanks with better performance than the reference control strategy, which is only effective for larger tanks. Additionally, a robustness analyses demonstrates that the mixed-integer model predictive controller can handle errors in the heat load prediction from the consumption level. Both analyses show promising results for the practical use of the proposed controller within the hierarchical control concept or as a control module in a similar but more general application.

Concept of Chaos-Based Hierarchical Network Control and Its Application to Transmission Rate Control

Concept of Chaos-Based Hierarchical Network Control and Its Application to Transmission Rate Control

A novel proxy signature scheme based on user hierarchical access control policy

In this paper, we propose a new security protocol for proxy signature by a hierarchy of proxy signers. In this protocol, the original signer delegates his/her signing capability to a predefined hierarchy of proxy signers. Given the documents of a security class to be signed by the original signer, our scheme suggests a protocol for the hierarchy of proxy signers to sign the document on behalf of the original signer. The concept of hierarchical access control limits the number of people who could sign the document to the people who have the required security clearances. User in a security class requires two secret keys: one which identifies his/her security clearance, and that can also be derived by a user of upper level security clearance and second is his/her private key which identifies him/her as a proxy signer for the signature generation. We show that our scheme is efficient in terms of computational complexity as compared to the existing related proxy signature schemes based on the hierarchical access control. Our scheme also supports addition and deletion of security classes in the hierarchy. We show through security analysis that our scheme is secure against possible attacks. Furthermore, through the formal security analysis using the AVISPA (Automated Validation of Internet Security Protocols and Applications) tool we show that our scheme is also secure against passive and active attacks.

Hierarchical Control Based Virtual Coordinated Synchronization of Chemical Auto Catalytic Reaction Networks

This paper suggests the concept of hierarchical control based virtual coordinated synchronization of chemical auto catalytic reaction networks. Under the new framework, the virtual coordinated variable is introduced, which is the average of the ensemble of the corresponding auto catalytic reaction networks, and on account of that, synchronization becomes possible. Unlike the already existing results, the average of the virtual coordinated variable is injected into the every auto catalytic reaction networks. And for the virtual coordinated construction has a lot of flexibility, so the suggested scheme can be easily extended to the multi-purposes control of the auto catalytic reaction networks.

Secondary Control Scheme for Voltage Unbalance Compensation in an Islanded Droop-Controlled Microgrid

The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme is proposed which includes primary and secondary control levels. The primary level comprises distributed generators (DGs) local controllers. The local controllers mainly consist of power, voltage and current controllers, and virtual impedance control loop. The central secondary controller is designed to manage the compensation of voltage unbalance at the point of common coupling (PCC) in an islanded microgrid. Unbalance compensation is achieved by sending proper control signals to the DGs local controllers. The design procedure of the control system is discussed in detail and the simulation results are presented. The results show the effectiveness of the proposed control structure in compensating the voltage unbalance.

Model-based trajectory planning, optimization, and open-loop control of a continuous slab reheating furnace

Abstract A temperature control method is developed for reheating steel slabs in an industrial furnace. The work was motivated by the need for mathematically simple furnace control schemes that feature accuracy, robustness, applicability to online control, and capabilities of non-steady-state operating scenarios, where the temperature goals and other properties of the slabs may vary considerably. The proposed hierarchical control concept computes desired heat inputs for each individual slab based on a discrete-time nonlinear model. Then, a quadratic program is solved to plan reference trajectories of furnace temperatures which optimally realize the desired heat inputs into the slabs. The iterative algorithm accounts for constraints on system inputs as well as states and may be used for open-loop control or as a feedforward branch in two-degrees-of-freedom control structures. The feasibility and the limitations of the approach are demonstrated by means of an example problem.

Control Strategy for Small-Scale Wood Chip Combustion

The purpose is to control small-scale (< 1MW th ) wood chip combustion in an inexpensive and durable way. Therefore, a hierarchical control concept is presented. The main task of the fuel feed control system, which is based on temperature and lambda measurements, is to settle the fuel feed to air feeds and to compensate for the temporary fluctuations in the fuel feed. The task of the air flow control is to set the primary and secondary air flows suitable for the power level and for the fuel moisture content. Test results of a 200 kW commercial system are presented. The process experiments indicate that the high level control system is able to adapt to varying combustion conditions and to maintain low emission levels. The control concept is adaptable also to existing systems.

Distributed intelligence in autonomous multi-vehicle systems

To make better use of existing infrastructures, new control methods are under development. In the Intelligent Infrastructures programme, an infrastructure is seen as a multi-agent system, with more or less autonomous subsystems that are related to each other in hierarchical, coordinated, cooperative, or non-cooperative way. Current controls for multi-vehicle systems are based on the hierarchical control concept. In this paper, it is shown how the incident handling, efficiency, and flexibility of multi-vehicle systems can be improved by applying a cooperative control strategy. An existing multi AGV application in a seaport illustrates that efficiency of operations can be improved considerably with smarter control. Finally, a research project is introduced concerning cooperative multi-agent control of true free-ranging automated guided vehicles.

Flatness-based control of a machine tool with lambda kinematic

In this paper the possibilities of a flatness-based control system for a new high-dynamic machine tool with lambda kinematic and lightweight components are investigated. For this purpose, the inverse kinematics of the machine tool is analyzed and a multibody system model is developed. Based on the model the flatness of the system is verified and subsequently a flatness-based quasi-static controller is developed. Simulation results are shown for open- and closed-loop control. The nonlinear control system will be used as basis for a hierarchical control concept with active vibration damping in order to compensate system vibrations due to elasticities in the real machine, which is available for experiments.

The workload control concept: theory and practical extensions of Load Oriented Order Release

Workload control (WLC) has been elaborated in the early 1980s to a hierarchical production control concept for job shop manufacturing. In the 1990s the analytical research at the University of Groningen focused on assessing the strengths and weaknesses of this concept and on developing alternatives. Research at the University of Hannover focused on improving the practical applicability of the WLC concept. While the practical experiences confirm the strengths of the WLC concept, some extensions of the basic concept have been developed which may overcome some weaknesses suggested in literature. This paper aims at bringing the theoretical and practical knowledge regarding the WLC concept together. It gives a review and classification of strengths and weaknesses reported from analytical research and it discusses the extensions that have been developed based on practical experiences.

Control and Parameter Optimization of Flexible Robots1*

A hierarchical control concept for flexible robot manipulators is presented. The equations of motion are derived using the multibody system method, incorporating flexible links equipped with surface bonded actuating and sensing devices. Exploiting the structure of the dynamic model, the control concept allows combination of any joint level control for the gross motion of the manipulator with decentralized linear control of the elastic deformation of each flexible link. Therefore, the approach is capable of solving both the problem of fast and precise point-to-point motion, with acceptable vibration characteristics, and the problem of accurate trajectory tracking of the end-effector. Control parameters are found through parameter optimization. In order to verify the proposed control strategy, a SCARA robot with one flexible link is considered.

Plant-Wide Control Concepts on the Basis of the Qualifying Potential

In this paper some plant-wide control concepts are discussed based on an extensive thermodynamic state function, the so-called qualifying potential. The dynamic plant behavior with respect to the production objective is represented by the balance equation of the qualifying potential. This concept enables an information compression and forms the basis for plant-wide quality control. The complex plant-wide control task is split into two parts using a hierarchical control concept with two levels. This facilitates the controller design and allows to achieve quality assurance of the end product. Connections between process control and process design are pointed out and the usefulness of the qualifying potential for both is shown.

Process design and control for quality assurance

In this paper a hierarchical process control concept for plant-wide quality control is proposed. The concept is based on a formal definition of product quality as an intensive state function in the thermodynamic sense. This quality function is evaluated for each product stream in a chemical plant and can be used as a plant-wide uniform controlled variable. For the assigned extensive state function, called the qualifying potential, a balance equation can be formulated and thus, the production of qualifying potential can be determined for each processing unit of a plant. Therefore, the quality concept can be used for process design as well as for process control.

Video encoder architecture for MPEG2 real time encoding

A video encoder architecture for encoding digital video signals based on the MPEG2 video standard up to the slice level is described. A function specific architecture is implemented to increase the coding efficiency and reduce the silicon area for real time encoding. A hierarchical control concept is adopted and a three-stage pipeline encoding method is used in the macroblock coding to increase the flexibility of the encoding flow and reduce the design effort. Most of the computing power for the MPEG2 encoding algorithm is utilized in motion estimation, so a separate motion estimation module is used as a coprocessor. The motion estimation algorithm adopted is a full search with the search window in the range between +47 and -48 pels in the horizontal direction and between +15 and -16 pels in the vertical direction. Simulations on several video sequences with different target bit rates are evaluated. The results show that our implementation can achieve a video quality comparable to other off-line software simulation programs using exhaustive searches.

Some aspects of integrated process operation

Operation and control of integrated processes is considered. Thereby, the aspect of process integration is examined on two levels. On the lower level, different unit operations, like reaction and heat recovery or reaction and separation, are integrated into multifunctional processing units. On the flowsheet level, different processing units are integrated via mass and energy recycles, like the heat integration of distillation columns. On both levels, complex dynamics including periodic and aperiodic oscillations and multiple attractors can arise as a conseqience of strong interaction. For the lower level, nonlinear phenomena are illustrated with two examples. The first example is the so-called circulation loop reactor, which is intended to work as an autonomous periodic system. Second, dynamic operation of a reactive distillation column with multiple steady states is considered. To handle dynamics on the flowsheet level a hierarchical process control concept for plant-wide control is presented. The concept is based on a formal definition of product quality as an intensive state function in the thermodynamic sense. This quality function is evaluated for each product stream in a chemical plant and is employed as a plant-wide controlled variable. Further, such a plant-wide objective function can be used for the integration of process design and control.