Reduced‐order LQG/LTR procedure for the plant output side

It is commonly believed that reduced‐order observers, including reduced‐order Kalman filters, cannot be used in the loop transfer recovery (LTR) design of the plant output side. In contrast to common understanding, we show that, at least for nonminimum‐phase plants, the reduced‐order Kalman filter can be used in the linear‐quadratic‐Gaussian (LQG)/LTR design of the plant output side with clear meaning in systems theory. The key concept is to regard a reduced‐order Kalman filter as a high‐gain full‐order Kalman filter. For the reduced‐order LQG controller, we examine the asymptotic property achieved by applying the recovery procedure used in the full‐order LQG/LTR design. Using the equivalent full‐order Kalman filter, we find that the sensitivity property of the reduced‐order LQG controller is asymptotically equivalent to that of a high‐gain partial output injection system. Motivated by this result, we propose the reduced‐order LQG/LTR procedure taking the high‐gain partial output injection system as a target. Some target properties are discussed to clarify the difference from the full‐order design. A multivariable design example is presented to show that the procedure provides a systematic design of a reduced‐order controller with optimality consideration.     

The design of dynamic ship positioning control systems using stochastic optimal control theory

The design of dynamic ship positioning control systems and their associated wave filters is considered. The control problems and the basic components in the system are discussed first. The model of the vessel is then described, since this plays an important role in the design of the Kalman filter which is used to estimate the low frequency motions of the vessel. The model involves both high and low frequency subsystems. The total linearized model for the vessel is represented by state equations, and simulation results are given to illustrate the performance of the Kalman filter. A comparison with a notch filter is also presented. The design of the optimal control system using LQG stochastic control results is considered. The operation of the system under various operating conditions is illustrated. Schemes involving the extended Kalman filter are then described. These enable more realistic non-linear models of the plant to be employed within the filter. This is shown to be unnecessary in the case of the low frequency ship model. However, the extended filter may be useful to track varying wave conditions (using parameter estimation) as represented in the high frequency model. Two extended filtering schemes are presented for this case.     

A multiobjective optimization approach for linear quadratic Gaussian/loop transfer recovery design

This article bestows the linear quadratic Gaussian (LQG)/Loop Transfer Recovery (LTR) optimal controller design for a perturbed linear system having insufficient information about systems states through a multiobjective optimization approach. A Kalman filter observer is required to estimate the unknown states at the output from the noisy data. However, the main downside of the LQG controller's is that its robustness cannot be guaranteed because it consists of linear quadratic regulator (LQR) and Kalman observer, and due to observer incorporation within the LQR framework results in loss of robustness which is undesirable. Therefore, it is necessary to recover the robustness by tuning the controller which further plays havoc with system performance and control effort for certain plants. The present work addresses the investigation of the trade-off between multiobjective indexes (formulated on the basis of robustness, optimal control, and performances) through three multiobjective optimization algorithms as NSGA-II, multiobjective simulated annealing and multiobjective particle swarm optimization. The tuned parameters meet the competitive multiobjective performance indexes that are verified through simulation results. The Pareto front with multiple solutions helps to design a robust controller depending on the weightage given to the respective performance indexes. Simulation results reveal that the proposed multiobjective control strategy helps in recovering the characteristics of LQG/LTR.     

Dissipative filter design for discrete-time interval type-2 fuzzy singular systems with mixed delays

In this article, the problem of delay-dependent dissipative filter design is studied for discrete-time interval type-2 (IT-2) fuzzy singular systems with both external disturbance and mixed delays. Two kinds of delays are considered, namely time-varying discrete delays and infinite distributed delays. First, considering the uncertainties in the membership functions, the nonlinear singular system and the filter are modeled by the IT-2 fuzzy systems. Then, based on new matrix inequalities dealing with the mixed delays, a new delay-dependent criterion is proposed to ensure the IT-2 fuzzy filtering error system is to be admissible with strictly dissipative performance. The filter parameters are characterised by the solution of linear matrix inequalities (LMIs). The feasibility of these results are verified by a numerical example.     

Feasibility of disturbance-accommodating control in steering of a large tanker

The feasibility of applying disturbance-accommodating control (DAC) techniques to the problem of steering control of a large tanker in a seaway is examined. A performance criterion representative of propulsion losses related to steering is used as a basis for the design of course-keeping controllers. The development of disturbance state models to take advantage of the short-term regularity of the seaway within a DAC framework is presented. Comparisons are made between the performance resulting from the DAC approach and previous LQG approaches to the problem using computer simulation results. On this basis, it is shown that controller design within a DAC framework may be a viable alternative to existing Kalman filter estimation/control schemes used in autopilot design.     

A comparison of two epidural catheter connectors

Background

Disconnection of the filter from its catheter is an established problem with epidural analgesia. Previously, it has been hypothesised that the screw cap connector is more prone to disconnection than the clamp connector design. The aim of this study was to test which of two mechanisms connecting the epidural catheter and filter was more prone to disconnection.

Methods

We recruited 20 consultant anaesthetists. First, each was asked to assemble an epidural set, either B Braun or Portex, in their normal way. Second, each anaesthetist assembled an epidural set, either B Braun or Portex, but was asked if they could improve the security of the connection, whilst avoiding catheter lumen occlusion. Each assembled set was then tested to determine adequacy of catheter connection using a standard protocol. Statistical analysis was performed using the Fisher’s exact test.

Results

The strength of the connection of the B Braun epidural set was similar to the Portex set when assembled for everyday practice (mean 1100 g; median 1100 g; SD 249 vs. mean 920 g; median 1050 g; SD 603). However, the incidence of inadequate connection was 0 in the B Braun group vs. 5 (25%) in the Portex group (P = 0.04). It was possible to improve the reliability of the Portex system, although episodes of weak connection were not eliminated.

Conclusions

We conclude that the Portex connection system is more prone to disconnection and that connection design is an important consideration when trying to minimise catheter disconnection.     

Controller design for optimal tracking response in discrete‐time systems

The problem of designing a controller, which results in a closed‐loop system response with optimal time‐domain characteristics, is considered. In the approach presented in this paper, the controller order is fixed (higher than pole‐placement order) and we seek a controller that results in closed‐loop poles at certain desired and pre‐specified locations; while at the same time the output tracks the reference input in an optimal way. The optimality is measured by requiring certain norms on the error sequence—between the reference and output signals—to be minimum. Several norms are used. First, l₂‐norm is used and the optimal solution is computed in one step of calculations. Second, l_∞‐norm (i.e. minimal overshot) is considered and the solution is obtained by solving a constrained affine minimax optimization problem. Third, the l₁‐norm (which corresponds to the integral absolute error‐(IAE)‐criterion) is used and linear programming techniques are utilized to solve the problem. The important case of finite settling time (i.e. deadbeat response) is studied as a special case. Examples that illustrate the different design algorithms and demonstrate their feasibility are presented. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimal parametrized design of thermal diffusers for communication satellites

The object of this paper is to present recent developments in the design of mass-optimized thermal diffusers with a priori specifications on the input power flux and a bound on the output power flux. This problem arises in connection with the use of high power solid state devices (HPSSD's) in future Canadian communication satellites. Delfour, Payre and Zolésio^1,2 have obtained results on the optimal design using the techniques of shape optimal design.^3-8 In this paper, we also consider suboptimal designs (e.g. doublers) and compare them with the optimal one. A similar problem has been studied by Destuynder.⁹ However, the present design differs in that we have a constraint on the normal derivative on a piece of the boundary surface instead of a constraint on the maximum temperature in the domain or body of the diffuser.     

Robust extended Kalman filtering for nonlinear systems with multiplicative noises

In this paper, we investigate the robust filter design problem for nonlinear systems with multiplicative noises. The aim of the problem is to design a state estimator with a predictor–corrector structure, such that the upper bound on the state estimation error variance is minimized. A robust extended Kalman filter (REKF) is proposed based on a novel method to obtain the upper bound on the variances of the multiplicative noises. Further analysis shows that the proposed filter guarantees a bounded energy gain from the multiplicative noises to the estimation error. The REKF is implemented on the satellite attitude determination system that consists of the gyroscopes and the star sensors. Its performance is illustrated by using the real data obtained from a gyroscope. Simulation results show that the REKF outperforms another robust algorithm. Copyright © 2010 John Wiley & Sons, Ltd.     

Further development of an approximate loop transfer recovery methodology for fixed order dynamic compensator design

This paper further develops a methodology for designing fixed order compensators. The formulation uses an approximate loop transfer recovery (LTR) method to achieve performance and stability subject to a disturbance and unstructured uncertainty at either the plant input or the plant output. The approximate LTR methodology has the advantage that the quadratic performance index weighting matrices are uniquely defined. To reduce sensitivity to real parameter uncertainty, the performance index is modified to include a penalty on the closed-loop sensitivity dynamics. The formulation avoids the explicit introduction of sensitivity states into the performance index and thus does not increase the overall dimension of the problem. An example design for the coupled mass benchmark control problem is provided to demonstrate this methodology.     

A combined state and state estimate feedback solution to the ship positioning control problem

A stochastic linear quadratic optimal control problem is considered in which some of the plant states may be measured without a measurement noise component. This set of states are assumed to be associated with the plant inputs and force transducers. The optimal controller is shown to include state feedback from this part of the system. The states which cannot be measured are assumed to be combined in noisy output signal. The optimal controller corresponding to this second subsystem is shown to include a Kalman filter and state-estimate feedback. The combination of state and state-estimate feedback has the advantage that the dimension of the Kalman filter is equal to that of the second subsystem mentioned above. In the conventional solution to this problem, no states are assumed measurable, and the dimension of the Kalman filter is equal to the dimension of the complete system. In many industrial control problems, the combined control law enables a significant reduction in the dimension of the filter to be achieved. The technique has been proposed for use in dynamic ship positioning control systems, and this problem is discussed.     

Servo controller design based on frequency-dependent error

Variables to be controlled are usually taken from measured outputs. They may be filtered and the regulation of frequency-dependent error has been considered in the design of robust controllers. Anderson considered the frequency-dependent linear-quadratic (LQ) problem. The frequency-dependent weight he considered is restricted to the phase lag and lead type. This paper considers not only regulation of general frequency-dependent errors but also a servo controller tracking to a given reference signal in the presence of disturbances. The control law is determined either on the basis of the quadratic criterion function or by pole assignment in a region. The control law to assign poles in a region is derived from one designed for the corresponding discrete-time system obtained by bilinear transformation.     

Design of adaptive controllers using partial certainty equivalence principle

Optimal stochastic control problem for general non‐linear dynamic system with unknown parameters is considered. An approximative assumption, which has been named partial certainty equivalence (PCE) principle, is suggested for design of adaptive controllers of non‐linear and linear stochastic systems. For derivation of a suboptimal controller with the PCE principle the certainty equivalence (CE) assumption is used only for the part of the system states and unknown parameters. The PCE control policy has a simple form for linear systems with unknown parameters. It is suggested in the present paper to design adaptive dual control using the PCE assumption and bicriterial optimization to derive the adaptive controller with the optimal persistent excitation. Simulated examples are used to demonstrate the potential of the suggested method and its superiority over the generally used CE‐controllers. Copyright © 2004 John Wiley & Sons, Ltd.     

Variance‐constrained robust estimation for uncertain systems with multiple packet dropouts

This paper deals with variance‐constrained filtering problem in networked control systems (NCSs) with multiple packet dropouts. The system is subject to time‐invariant norm‐bounded parameter uncertainties in both the state and measurement matrices. Based on a model of multiple packet dropouts, the consecutive packet losses rate is transformed into a stochastic parameter in the system representation. The problem addressed is to design a linear filter such that, for all admissible parameter uncertainties and consecutive packet dropouts, the error state of the filtering process is mean square bounded, and the steady‐state variance of the estimation error for each state is not more than the individual prescribed upper bound. The conditions for the existence of a desired filter are obtained in terms of the solutions of two algebraic matrix inequalities, based on which an explicit expression of the robust filter is derived. Finally, an algorithm for solving the coupling inequalities, which is not optimal but practical, is provided and applied to some numerical examples. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimal design problems for curvilinear shallow elements of structures

New problem statements for the optimal design of thin-wall structural elements are considered by means of optimal control theory. The distribution of initial curvature of shallow curvilinear structural elements in a non-strain state is taken as the control function.^1–3 Integral stiffness is considered as the optimized performance index. The necessary optimality condition and the partial differential equations for the adjoint variables are derived. An analysis of these relations is carried out, and the initial optimal control problem is reduced to a boundary problem of the bending of an uncurved element. Problems of optimal design of plates under transverse loads, as well as under tensile or compression forces acting in the middle surface, are studied. Analogous problems of optimal design for shallow curvilinear plates on an elastic foundation are also investigated. Some two-dimensional analytical solutions for optimal plates under loads of different types are obtained.     

The acoustic filter: an ultrasonic blood filter for the heart-lung machine.

Cardiopulmonary bypass-associated encephalopathy is thought to be due in part to continuous microembolization of the brain with gas microbubbles more than 40 microns in diameter during bypass. Current barrier filter technology cannot effectively remove such small microbubbles in fragile fluids such as blood. The design concepts for a new nonbarrier ultrasound-based fluid filtration system (an "acoustic filter") capable of filtering small microbubbles from blood are presented. The acoustic filter uses a field of high-intensity ultrasound to push microbubbles down an acoustic gradient, where they can be collected and removed. To test the filtration efficiency of the system, a Doppler ultrasound bubble detector was built. By monitoring the prefilter and postfilter Doppler signal an assessment of filtration efficiency was made. A suspension of stable albumin-encapsulated microbubbles (4 to 32 microns) were used as a model of the microbubble contaminants that might be found in the arterial return line of the heart-lung machine. Inactivated, the acoustic filter neither removed nor added microbubbles to the fluid. Activated, the acoustic filter provided total or near-total clearing of microbubbles. We conclude that the acoustic filter can remove microbubbles from a cardiopulmonary bypass-like apparatus.     

Can preoperative gonadotropin and testosterone levels predict the success of varicocelectomy?

We examined the effects of preoperative hormonal values on varicocelectomy success. A total of 136 patients who underwent varicocelectomy for infertility in our clinic were analysed retrospectively. Improvement in semen quality was defined as >50% increase in post-operative total motile sperm count (TMSC) in those with preoperative TMSC >5 million and at least 100% increase in those with <5 million. The patients were divided into two groups as benefiting from the treatment (Group A) and no benefits (Group B). The best cut-off value for follicle-stimulating hormone (FSH) and the luteinising hormone/testosterone ratio (LTR) that can predict varicocelectomy success were 7.01 and 0.016 with an area under the curve of 0.844 and 0.856 respectively. The highest sensitivities and specificities of FSH and LTR were 0.845 and 0.788 and 0.821 and 0.846 respectively. Binary logistic regression analysis showed FSH (odds ratio [OR]: 3.7; p < .001) and LTR (OR: 5.2; p < .001) as independent predictive factors in predicting varicocelectomy success. Our study demonstrated that low FSH (7.01 IU/L) and LTR (<.016) can be a useful preoperative predictive tool to help identify men who benefit most from varicocelectomy in infertile patients with varicocele.     

Set‐valued observer‐based active fault‐tolerant model predictive control

This paper proposes an integrated actuator and sensor active fault‐tolerant model predictive control scheme. In this scheme, fault detection is implemented by using a set‐valued observer, fault isolation (FI) is performed by set manipulations, and fault‐tolerant control is carried out through the design of a robust model predictive control law. In this paper, a set‐valued observer is used to passively complete the fault detection task, while FI is actively performed by making use of the constraint‐handling capability of robust model predictive control. The set‐valued observer is chosen to implement fault detection and isolation (FDI) because of its simple mathematical structure that is not affected by the type of faults such as sensor, actuator, and system‐structural faults. This means that only one set‐valued observer is needed to monitor all considered actuator and sensor statuses (health and fault) and to carry out the fault detection and isolation task instead of using a bank of observers (each observer matching a health/fault status). Furthermore, in the proposed scheme, the advantage of robust model predictive control is that it can effectively deal with system constraints, disturbances, and noises and allow to implement an active FI strategy, which can improve FI sensitivity when compared with the passive FI methods. Finally, a case study based on the well‐known two‐tank system is used to illustrate the effectiveness of the proposed fault‐tolerant model predictive control scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

Endoscopic management of subglottic stenosis

OBJECTIVES: Determine the effectiveness of endoscopic surgical treatment of subglottic stenosis (SGS) in children as a primary surgical modality to prevent laryngotracheal reconstruction (LTR) and as treatment for restenosis following primary LTR to prevent revision LTR. PATIENTS: Children undergoing various endoscopic surgical treatments from 1989 to 2006 for SGS. RESULTS: The number of children and success rates per grade of SGS and the number of procedures required to produce a successful result in 29 children initially managed endoscopically included grade I, three of three (100%), 1.3 procedures; grade II, eight of nine (88%), 2.6 procedures; and grade III, 13 of 17 (76%), 3.5 procedures. Of 102 patients undergoing open LTR, 56 of 102 required endoscopic interventions and 41 of 56 (73%) children were treated successfully. CONCLUSION: Endoscopic intervention can be used to manage SGS either as a primary intervention or to treat reobstruction and restenosis following an open reconstructive procedure. Success rates decline as the severity of stenosis increases.     

Evidence-based used, yet still controversial: the arterial filter

Arterial line filters are considered by many as an essential safety measure inside a cardiopulmonary bypass circuit. There is no doubt that this was true during the bubble oxygenator era, but we can question whether the existing arterial line filter design and positioning of the filter are still optimal seeing the tremendous progress in cardiopulmonary bypass circuit components. This overview gives a critical overview of existing arterial line filter design.