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Control Theory and Applications, IEE Proceedings -

Issue 3 • Date 9 May 2006

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Displaying Results 1 - 16 of 16
  • Editorial - The second ALSTOM benchmark challenge on gasifier control

    Publication Year: 2006
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (46 KB)  

    The ALSTOM benchmark challenge on gasifier control II was initially launched by ALSTOM in 1992 and is now hosted by the IEE PN for control and automation on its website. The intention was to provide an industrially relevant control problem using which, researchers could implement and demonstrate their control methodologies. The challenge comprises a non-linear model of a coal gasifier, a set of control system design requirements and several test cases, which facilitate the comparison of different control designs upon a level playing field. In September 2004, the challenge was the focus of a special session of the UKACC Control 2004 Conference at the University of Bath. The presentations generated lively debate and the audience were able to participate in the evaluation of several control approaches as applied to a difficult industrial control problem. This editorial introduces a special section on the benchmark challenge problem, briefly describing each of the extended papers published in the section. View full abstract»

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  • Alstom Benchmark Challenge II on Gasifier Control

    Publication Year: 2006 , Page(s): 254 - 261
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (290 KB)  

    Gasification offers a clean and efficient method for producing gas from carbon-based feedstock such as high-sulphur fuel oil, refinery tars, petroleum coke, coal and biomass. The product gas can then be burnt cleanly and efficiently in a combined cycle gas turbine to produce electricity. The authors introduce the second ALSTOM Benchmark Challenge on Gasifier Control, in which a validated non-linear model of a coal gasifier was put forward as the subject of a control challenge to the research community. The challenge problem includes the operating constraints, disturbance characteristics, control specifications and closed-loop performance tests. A baseline Proportional+Integral controller is provided as part of the challenge for the purpose of comparison. The design methods used and performance results obtained for the baseline controller are described. View full abstract»

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  • Structure selection and tuning of multi-variable PID controllers for an industrial benchmark problem

    Publication Year: 2006 , Page(s): 262 - 267
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    A new technique is presented based on genetic algorithms (GAs) for designing a multi-variable PID controller. The considered application is a gasifier benchmark problem, for which a number of performance and robustness requirements are defined. In addition, actuator constraints are also considered. The proposed design procedure allows the optimisation of both controller parameters and structure. An advantage of the proposed technique over standard optimal control techniques (H2 and H methods) is its ability to take non-linear constraints and dynamics into account in the design algorithm in a straightforward manner. A disadvantage of the proposed technique is the potentially large computation time required by GA. To overcome this problem, the optimisation is performed over several stages. First the structure is optimised, then basic controllers are designed (only PI terms) and finally a derivative term is added if needed. Simulation results on the gasifier problem have confirmed the superiority of the proposed technique in terms of achieved performance and robustness; moreover, the computation time of the overall design procedure is significantly reduced when compared with a standard GA approach. A controller that meets all design objectives under all operating conditions, and satisfies all input-output constraints, is presented. View full abstract»

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  • State estimation-based control of a coal gasifier

    Publication Year: 2006 , Page(s): 268 - 276
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (331 KB)  

    On-line state estimation techniques provide a means of inferring real-time values for key process variables that cannot themselves be measured directly. Such state estimates can then form a basis for improved process control. Accordingly, Kalman filtering (KF) is applied to a non-linear coal gasifier system operated initially under a conventional feedback control strategy. Key unmeasured disturbances to gasifier operation arise in discharge pressure and coal feed 'quality'. The fact that by treating both of these variables as unknown process parameters, they can be included in an augmented state and parameter vector and estimated reliably by KF is shown. A proportional feedforward control strategy, acting on these disturbance estimates and linked into the existing conventional feedback control system, is then shown to enhance system performance to both step and sinusoidal discharge pressure changes and to steps of up to 18% around normal coal feed quality. No significant performance difference relative to conventional feedback control is shown in ramping the downstream-generated power output. An important future outcome may be enhanced operation and control of upstream coal preparation plant based on the capability demonstrated here to obtain reliable real-time estimates of coal quality by KF. View full abstract»

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  • Multivariable proportional-integral-plus (PID) control of the alstom nonlinear gasifier simulation

    Publication Year: 2006 , Page(s): 277 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (194 KB)  

    First Page of the Article
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  • Improving the performance of the ALSTOM baseline controller using multiobjective optimisation

    Publication Year: 2006 , Page(s): 286 - 292
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    The authors present a multiobjective optimisation design approach to improve the performance of the ALSTOM Benchmark Challenge baseline controller. As the gasifier process is complex and non-linear, with a high degree of cross coupling of the variables, manual tuning of the controllers is difficult. The use of a multiobjective optimisation method allows the simultaneous tuning of multiple controllers, seeking a trade-off between the different performance objectives. A further example using the same multiobjective optimisation method shows how the performance of the baseline controller can be improved by the addition of extra proportional controllers to reduce the fluctuation due to a sine-wave pressure disturbance. This control structure is then simplified using a genetic algorithm search procedure, to find the structure with the lowest error. View full abstract»

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  • Predictive control for the ALSTOM gasifier problem

    Publication Year: 2006 , Page(s): 293 - 301
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (206 KB)  

    Model predictive control (MPC) has become the first choice of control strategy in many cases especially in the process industry because it is intuitive and can explicitly handle MIMO (multiple input multiple output) systems with input and output constraints. The authors implemented a simple MPC algorithm based on the state space formulation to control the ALSTOM gasifier. Among three operating conditions of the plant, 0% load condition is identified as the worst case. A linearised state space model at 0% load condition of the non-linear plant is adopted as the internal model for performance prediction. Because of this choice, the control system comfortably achieves performance requirements at the most difficult load condition. Meanwhile, the case study shows that the model is also adequate to pass all tests under other load conditions specified in the benchmark problem. The MPC algorithm uses standard formulation and off-the-shelf software with a few tunable parameters. Thus, it is easy to implement and to tune to achieve satisfactory performance. View full abstract»

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  • Control of integral processes with dead time. Part IV: various issues about PI controllers

    Publication Year: 2006 , Page(s): 302 - 306
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (199 KB)  

    Various issues about integral processes with dead time controlled by a PI controller are discussed. First, the region of the control parameters to guarantee the system stability is characterised. Then, the control parameters to achieve the given gain and/or phase margins (GPM) are determined. Furthermore, the constraint on achievable GPM is derived. These results are obtained on the basis of the normalised system that involves only two free parameters. View full abstract»

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  • Delay-dependent guaranteed cost control for uncertain systems with state and input delays

    Publication Year: 2006 , Page(s): 307 - 313
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (141 KB)  

    The authors deal with the problem of delay-dependent guaranteed cost control for uncertain linear systems with time-varying delays in both the state and the input. The purpose of this is to design state-feedback controllers such that the resulting closed-loop system is robustly stable, and a specified linear integral-quadratic cost function has an upper bound for all delays in the given intervals. Two types of the time-varying delays are considered. Delay-dependent sufficient conditions for the solvability of the problem are developed in terms of matrix inequalities. By the cone complementary linearisation method, desired state-feedback controllers can be constructed. A numerical example is provided to demonstrate the applicability of the proposed method. View full abstract»

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  • Computational framework for digital input shapers using linear optimisation

    Publication Year: 2006 , Page(s): 314 - 322
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (294 KB)  

    Numerous types of input shapers have been developed to reduce motion-induced vibration. Many of the shapers are designed using non-linear optimisation methods that can be challenging to implement and do not guarantee a global minimum solution. This paper unifies the solution of different types of input shapers into a single computational framework based on linear optimisation techniques. Two methods for computing a variety of digital input shapers are presented. The first method is a multi-level optimisation that enables both primary and secondary performance measures to be simultaneously optimised. The second method is a computationally efficient technique for computing very robust shapers. View full abstract»

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  • Design of a repetitive controller: an application to the track-following servo system of optical disk drives

    Publication Year: 2006 , Page(s): 323 - 330
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    In an optical disk drive servo system, disturbances with significant periodic components cause tracking errors of a periodic nature. As an effective control scheme for improving periodic disturbance attenuation performance, repetitive control has been applied successfully to the track-following servo system of optical disk drives. The increase in disk rotational speed to achieve a better data throughput leads to the increase in the frequency of periodic disturbance, which needs a high loop gain in a wider control bandwidth. However, this requirement is not easily accomplished because plant uncertainty hinders selecting the bandwidth of a filter in the repetitive controller. The problem of add-on type repetitive controller design for a track-following servo with norm-bounded uncertainties in optical disk drives with high rotational speed is examined. Using the Lyapunov functional for time-delay systems, a sufficient condition for robust stability of the repetitive control system is derived in terms of an algebraic Ricatti inequality or a linear matrix inequality (LMI). On the basis of the derived condition, it is shown that the repetitive controller design problem can be reformulated as an optimisation problem with an LMI constraint on the free parameter. The validity of the proposed method is verified through experiments using a DVD-ROM drive. View full abstract»

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  • Application of feedback linearisation to the tracking and almost disturbance decoupling control of multi-input multi-output nonlinear system

    Publication Year: 2006 , Page(s): 331 - 341
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    The tracking and almost disturbance decoupling problem of multi-input multi-output nonlinear systems based on the feedback linearisation approach are studied. The main contribution of this study is to construct a controller, under appropriate conditions, such that the resulting closed-loop system is valid for any initial condition and bounded tracking signal with the following characteristics: input-to-state stability with respect to disturbance inputs and almost disturbance decoupling, that is, the influence of disturbances on the L2 norm of the output tracking error can be arbitrarily attenuated by changing some adjustable parameters. One example, which cannot be solved by the first paper of the almost disturbance decoupling problem on account of requiring some sufficient conditions that the nonlinearities multiplying the disturbances satisfy structural triangular conditions, is proposed to exploit the fact that the tracking and the almost disturbance decoupling performances are easily achieved by the proposed approach. To demonstrate the practical applicability, a famous half-car active suspension system has been investigated. View full abstract»

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  • Feature-aided tracking with GMTI and HRR measurements via mixture density estimation

    Publication Year: 2006 , Page(s): 342 - 356
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1606 KB)  

    Tracking ground moving targets with ground moving target indicator and high resolution range (HRR) measurements is becoming increasingly important for many military and civilian applications. We first propose a new HRR information exploitation method using the technique of mixture density estimation. With this technique, features extracted from HRR profiles include not only peak locations and magnitudes, but also the information regarding how energy spreads around peaks. Therefore it is expected to increase significantly the feature discrimination power. We then develop a feature-aided tracking (FAT) algorithm that combines HRR features with traditional kinematic measurements in a probabilistic way. The algorithm does not require any a priori knowledge of target identifications. Simulation results are presented for both the HRR feature extraction method and the FAT algorithm. View full abstract»

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  • Pole assignment for uncertain symmetric circulant composite systems in a specified disk

    Publication Year: 2006 , Page(s): 357 - 363
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (154 KB)  

    Regional pole assignment for a kind of uncertain symmetric circulant composite system by state feedback in a specified disk is discussed. The 'decentralised D stabilisation controllers' have been obtained by making use of the special structure of the system. Thus the problem of assigning the poles in a specified disk for such an uncertain system with N · n dimensions can be transformed into the subproblems for N/2+1 or (N+1)/2 uncertain systems with n dimensions. The central D stabilisation controller for such a system has the same block symmetric circulant structure as the original system and can be constructed by the 'decentralised D stabilisation controllers'. View full abstract»

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  • Optimal life-extending control of a boiler system

    Publication Year: 2006 , Page(s): 364 - 370
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (159 KB)  

    The objective of life-extending control (LEC), also known as damage-mitigating control, is to design a controller to achieve a good tradeoff between structural durability and dynamic performance in a system. This task involves both damage dynamics modelling and LEC design. The authors propose a new hierarchical LEC structure and apply it to a typical boiler system. There are two damage models in this structure: Model I is for on-line LEC, Model II is for on-line life prediction of the critical components of the system. Finally, an optimal LEC scheme is proposed and simulation results show that the designed LEC substantially reduces the accumulated damage with a minimum loss of dynamic performance. View full abstract»

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  • Kalman filtering with inequality constraints for turbofan engine health estimation

    Publication Year: 2006 , Page(s): 371 - 378
    Cited by:  Papers (22)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (185 KB)  

    Kalman filters are often used to estimate the state variables of a dynamic system. However, in the application of Kalman filters some known signal information is often either ignored or dealt with heuristically. For instance, state-variable constraints (which may be based on physical considerations) are often neglected because they do not fit easily into the structure of the Kalman filter. Thus, two analytical methods to incorporate state-variable inequality constraints into the Kalman filter are now derived. The first method is a general technique that uses hard constraints to enforce inequalities on the state-variable estimates. The resultant filter is a combination of a standard Kalman filter and a quadratic programming problem. The second method uses soft constraints to estimate those state variables that are known to vary slowly with time. (Soft constraints are constraints that are required to be approximately satisfied rather than exactly satisfied.) The incorporation of state-variable constraints increases the computational effort of the filter but significantly improves its estimation accuracy. The improvement is proven theoretically and simulations are used to show that the proposed algorithms can provide an improved performance over unconstrained Kalman filtering. View full abstract»

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