Control Systems Design

Oil and gas industry processes are associated with significant expenditures and risks. Adequacy of the decisions on safety measures made during early stages of planning the facilities and processes contributes to avoiding technological incidents and corresponding losses. Formulating straightforward requirements for safety instrumented systems that are followed further during the detailed engineering design and operations is proposed, and a mathematical model for safety system design is introduced in a generalized form. The model aims to reflect the divergent perspectives of the main parties involved in oil and gas projects, and, therefore, it is formulated as a multi-objective problem. Application of black box optimization is suggested for solving real-life problem instances. A Markov model is applied to account for device failures, technological incidents, continuous restorations and periodic maintenance for a given process and safety system configuration. This research is relevant to engineering departments and contractors, who specialize in planning and designing the technological solution.

A new model-based plasma current and shape controller has been set up and tested on the JET Tokamak with the existing active circuits and control. The installation has been carried out without causing any interference to the plasma operation and without requiring a long commissioning time. Eventually, the new controller was used on really extremely shaped internal transport barrier experiments at high poloidal beta and in the presence of quite large variations of the plasma current density profile (variation range Δβpol up to 1.5 and Δli up to 0.5). The extreme shape controller (XSC) controller architecture and philosophy also offer new interesting opportunities, e.g., the separatrix sweeping on the divertor plates without significantly affecting the overall plasma shape, and the possibility of improving the overall tokamak performance via combined control of plasma shape, current and profile. The adopted methodology constitutes also an important test bed for feedback control strategies of ITER relevance.

The need to achieve increasingly better performance in present and future tokamak devices has made plasma control increasingly important in tokamak engineering. When high performance and robustness are required, it is essential to adopt a model-based approach to design a control system. We introduce the basics of plasma current, position, and shape control in tokamaks. As an example, the plasma magnetic control systems of the JET tokamak is presented, together with an approach proposed for plasma axisymmetric magnetic control at the ITER tokamak.

This work shows the engineering process carried out for the design of a low cost control system for an astronomical observatory. The work describes the implementation to adapt the equipment of the observatory to a Master Control System (MCS) and be able to use it remotely. The instruments and software required for the integration of the equipment as part of a robotic observatory are also described.

As part of the ITER design review, a reassessment of the specifications underlying the design of the vertical stabilization system (VS) was performed. Recent results from experiments, aimed at the evaluation of the feasibility of the ITER reference scenarios, have raised several concerns regarding mostly the ramp-up and ramp-down phases of the pulse. The main issue is the value of the internal inductance li which may reach values outside the range 0.7–1, considered as reference for the ITER control system design. Similar ...

The paper is devoted to the problem of designing matrix regulators for a special class of multivariable feedback control systems called circulant systems. The exposition is based on the characteristic transfer function method, which allows reducing the investigation of N-dimensional multivariable control system to the investigation of N fictitious one-dimensional systems. An analytical formula for elements of circulant matrix regulators is derived.

As part of the ITER design review, a reassessment of the specifications underlying the design of the vertical stabilization system (VS) was performed.

Recent results from experiments, aimed at the evaluation of the feasibility of the ITER reference scenarios, have raised several concerns regarding mostly the ramp-up and ramp-down phases of the pulse. The main issue is the value of the internal inductance li which may reach values outside the range 0.7–1, considered as reference for the ITER control system design. Similar concerns apply to the low current L-mode plasmas, needed to the exploitation of the machine towards the development of the 15 MA pulse. The performance of the reference vertical stabilization system, under the revised conditions may be marginal, in particular if the effect of plasma generated noise on the velocity measurement is considered.

A reliable and robust VS is mandatory to guarantee the operation of ITER at the reference elongation and plasma current values. To avoid de-scoping of the machine mission, several solutions have been proposed to improve the VS performances, ranging from an upgrade of the maximum voltage available to the present external coils system, to the introduction of in-vessel passive and/or active conductors.

The paper presents an overview of the modelling and experimental effort aimed at the assessment of the baseline ITER VS and analyses the proposed solutions to improve the system performance.

In this paper, we revisit the dynamic allocation scheme for input redundant plants proposed in Zaccarian (2009). within a set-point regulation setting and propose generalizations that apply to cases where the plant under consideration is not input redundant but the control specifications allow us to modify the set-point regulation within certain bounds. In this case, the input allocator is extended to the nonredundant case by allowing it to improve the input allocation selection at the price of some output regulation error. We also establish here desirable convergence properties of the allocator, which were only addressed for the linear case in Zaccarian (2009). In particular, we design the allocator dynamics as the gradient of a cost function and establish its convergence to the minimum of the cost function under some mild conditions. The allocation scheme is applied to the JET tokamak shape controller by illustrating its capabilities to enforce coil currents selections that tend to move away from the saturation limits within the allowable degrees of freedom.

Frequency-domain methods have provided an established approach to the analysis and design of single-loop feedback control systems in many application areas for many years. Individual Channel Analysis and Design (ICAD) is a more recent development that allows neo-classical frequency-domain analysis and design methods to be applied to multi-input multi-output control problems. This paper provides a case study illustrating the use of the ICAD methodology for an application involving liquid-level control for a system based on two coupled tanks. The complete nonlinear dynamic model of the plant is presented for a case involving two input flows of liquid and two output variables, which are the depths of liquid in the two tanks. Linear continuous proportional plus integral controllers are designed on the basis of linearised plant models to meet a given set of performance specifications for this two-input two-output multivariable control system and a computer simulation of the nonlinear mod...

The paper is devoted to the problem of designing matrix regulators for a special class of multivariable feedback control systems called circulant systems. The exposition is based on the characteristic transfer function method, which allows reducing the investigation of N - dimensional multivariable control system to investigation of N fictitious one-dimensional systems. An analytical formula for elements of circulant matrix regulators is derived. Դիտարկվում է հետադարձ կապով բազմաչափ կառավարման համակարգերի հատուկ դասի, այսպես կոչված, ցիրկուլյանտ համակարգերի մատրիցային կարգավորիչների նախագծման խնդիրը: Ներկայացվածը կատարված է բնութագրիչ փոխանցման ֆունկցիաների մեթոդով, որը թույլ է տալիս N –չափանի փոխադարձ կապերով կառավարման համակարգերի հետազոտումը հանգեցնել մեկ մուտքով և ելքով N հատ երևակայական համակարգերի հետազոտման: Դուրս է բերված անալիտիկ բանաձև` ցիրկուլյանտ մատրիցային կարգավորիչի տարրերի որոշման համար: Рассматривается задача проектирования матричных регуляторов для специального клас...

In the paper the design of an aircraft motion controller based on the Dynamic Contraction Method is presented. The control task is formulated as a tracking problem for Euler angles, where the desired decoupled output transients are accomplished under assumption of high-level, high-frequency sensor noise and incomplete information about varying parameters of the system and external disturbances. The resulting controller has a simple form of a combination of a low-order linear dynamical system and a matrix whose entries depend nonlinearly on certain measurable flight variables.

There has been a renewed interest in multiobjective control system design using parameter search techniques. One multiobjective approach is the method of inequalities, where the problem is formulated as a set of algebraic inequalities which must be satisfied for a successful design. In this paper, the performance of three algorithms which can be used to solve inequalities are compared. Two of the algorithms are based on hill-climbing techniques, whilst the third uses a genetic algorithm (GA) approach

The ITER Central Interlock System (CIS) executes manual and automatic interlocks in order to protect tokamak’s investments. When a new control system, such as the CIS, has to be deployed, it is strongly recommended to use modeling and simulation tools, in order to test and validate the control logics. This paper presents the software tools that have been recently developed to perform the modeling of the ITER CIS. In particular, the architectures of both a CIS oriented plant simulator and of a CIS logical prototype are presented, together with the simulation of two test cases.

The international thermonuclear experimental reactor (ITER) is the next step toward the realization of electricity-producing fusion power plants. ITER has been designed so as to reach the plasma burning condition, and to operate with high elongated unstable plasmas. However, due to the constraints which affect the machine realization, these open-loop unstable high performance plasmas can be hardly stabilized using the Poloidal Field coils placed outside the tokamak vessel. In this paper, it is proposed to use the in-vessel coils to vertically stabilize the plasma. In particular a constraint on the current in the in-vessel coils is explicitly taken into account in the design procedure, so as to yield a controller which can operate safely. Furthermore, the proposed controller is designed as a static-output feedback, in order to obtain a simple structure which permits to envisage effective adaptive algorithms, as it is usually required in operating tokamaks. The sufficient condition provided to design the controller is expressed in terms of a Bilinear Matrix Inequalities feasibility problem. The effectiveness of the approach is shown in a study case.