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Papers by Asier Hernandez

Research paper thumbnail of On the asymptotic hyperstability of switched systems under integral-type feedback regulation Popovian constraints

IMA Journal of Mathematical Control and Information, 2014

Asymptotic hyperstability is achievable under certain switching laws if at least one of the feedf... more Asymptotic hyperstability is achievable under certain switching laws if at least one of the feedforward parameterization: 1) possesses a strictly positive real transfer function, 2) a minimum residence time interval is respected for each activation time interval of such a parameterization, and 3) a maximum allowable residence time interval is guaranteed for all active parameterization which is not positive real.

Research paper thumbnail of Robust Sliding Control of SEIR Epidemic Models

Mathematical Problems in Engineering, 2014

This paper is aimed at designing a robust vaccination strategy capable of eradicating an infectio... more This paper is aimed at designing a robust vaccination strategy capable of eradicating an infectious disease from a population regardless of the potential uncertainty in the parameters defining the disease. For this purpose, a control theoretic approach based on a sliding-mode control law is used. Initially, the controller is designed assuming certain knowledge of an upper-bound of the uncertainty signal. Afterwards, this condition is removed while an adaptive sliding control system is designed. The closed-loop properties are proved mathematically in the nonadaptive and adaptive cases. Furthermore, the usual sign function appearing in the sliding-mode control is substituted by the saturation function in order to prevent chattering. In addition, the properties achieved by the closed-loop system under this variation are also stated and proved analytically. The closed-loop system is able to attain the control objective regardless of the parametric uncertainties of the model and the lack of a priori knowledge on the system.

Research paper thumbnail of Partial stability of controlled SEIR epidemic models

This paper proposes to use the concept of partial stability instead of that of global stability t... more This paper proposes to use the concept of partial stability instead of that of global stability to analyze the dynamic behavior of epidemic models. The rationale behind this is that it is only needed, from a practical point of view, to ensure the boundedness of the infectious and infected subpopulations in order to get the disease under control. Thus, the partial stability of a controlled SEIR epidemic model is studied in the vaccination-free case. It will be proved that the infectious and infected subpopulations may still be bounded when the total population increases and global stability is not achieved. In addition, a feedback-based vaccination policy is designed based on the concept of partial stability of the closed-loop system. Some numerical simulations illustrating the usefulness of the designed control law along with a comparison with previous vaccination laws complete the paper.

Research paper thumbnail of A pole-placement based scheme for robustly stable adaptive control of continuous linear systems with multiestimation

Proceedings of the 20th IEEE International Symposium on Intelligent Control, ISIC '05 and the 13th Mediterranean Conference on Control and Automation, MED '05, 2005

This paper deals with the pole-placement type robust adaptive control of continuous linear system... more This paper deals with the pole-placement type robust adaptive control of continuous linear systems in the presence of bounded noise and a common class of unmodeled dynamics with the use of multiple estimation schemes working in parallel. The multiestimation scheme consisting of the above set of various single estimation schemes is a tool used to minimize the plant identification error by building an estimate which is a convex combination of the estimates at all time. The weighting functions of the individual estimates are provided at each time by a suboptimization scheme for a quadratic loss function of a possibly filtered tracking error and / or control input. The robust stability of the overall adaptive scheme is ensured by an adaptation relative dead zone which takes into account the contribution of the unmodeled dynamics and bounded noise. The basic results are derived for two different estimation strategies which have either a shared regressor with the plant or individual regressors for the input contribution and its relevant time-derivatives. In this second case, the plant input is obtained through a similar convex combination rule as the one used for the estimators in the first approach.

Research paper thumbnail of Control adaptable discreto con esquema de multiestimación en paralelo con incorporación de técnicas de supervisión e inteligencia artificial. Aplicaciones al control de manipuladores robóticos

Research paper thumbnail of Control adaptable discreto con esquemas de multiestimación en paralelo con incorporación de técnicas de supervisión e inteligencia artificial. Aplicaciones al control de manipuladores robóticos

Research paper thumbnail of A time-varying SIS epidemic model with incidence rate depending on the susceptible and infective populations with eventual impulsive effects

Applied Mathematics and Computation, 2013

This paper is concerned with a SIS (susceptible, infected and susceptible populations) propagatio... more This paper is concerned with a SIS (susceptible, infected and susceptible populations) propagation disease model with a nonlinear incidence rate and eventual impulsive (non-necessarily being simultaneous) culling of both populations. The disease transmission does not necessarily take into account the total population as a normalizing effect. In this sense, the considered model is a mixed pseudo-mass. The positivity, stability of both the impulse-free and impulsive under pulse culling variants of the model are investigated in this paper.

Research paper thumbnail of Multi-Model Smith Predictor Based Control of Multivariable Systems with Uncertain Bounded External Delays

IEEE Latin America Transactions, 2009

One of the drawbacks of the Smith Predictor (SP) to control systems with external point delays is... more One of the drawbacks of the Smith Predictor (SP) to control systems with external point delays is that its performance is strongly influenced by the knowledge of the time delay of the plant. Hence, as the mismatch between the actual delay of the plant and the nominal one used in the control structure increases, the closed-loop performance degrades accordingly, even potentially causing instability. This effect is particularly important when dealing with multivariable systems, where there is a coupling between input and output variables. In this paper, an intelligent frame to reduce the a priori knowledge of the plant delays required in the design of SP controllers for multivariable systems is proposed. The intelligent frame is composed of a set of different plant delay models running in parallel along with a high level supervision algorithm which selects the one that best describes the actual delay of the plant at each time interval to be used for control purposes. In this way, the designer can design the control of the system based on its delay-free part while the appropriate tuning of the delay of the Smith Predictor is performed by the intelligent supervisor. As a consequence, like simulation examples show, the closed-loop performance of the system is improved without the a priori requirement of an accurate knowledge of the value for the time delay.

Research paper thumbnail of Inventory control of supply chains: Mitigating the bullwhip effect by centralized and decentralized Internal Model Control approaches

European Journal of Operational Research, 2013

In this paper, a two-degrees-of-freedom Internal Model Control structure is incorporated in produ... more In this paper, a two-degrees-of-freedom Internal Model Control structure is incorporated in production inventory control for a supply chain system. This scheme presents an intuitive and simple parametrization of controllers, where inventory target tracking and disturbance (demand) rejection in the inventory level problems are treated separately. Moreover, considering that the lead times are known, this scheme presents a perfect compensation of the delay making the stabilization problem easier to handle. This control structure is formulated for a serial supply chain in two ways (by using a centralized and a decentralized control approach). The behavior of these inventory control strategies is analyzed in the entire supply chain. Analytical tuning rules for bullwhip effect avoidance are developed for both strategies. The results of controller evaluations demonstrate that centralized control approach enhances the behavior with respect to the inventory target tracking, demand rejection and bullwhip effect in the supply chain systems.

Research paper thumbnail of Asymptotically non-expansive self-maps and global stability with ultimate boundedness of dynamic systems

Applied Mathematics and Computation, 2013

This paper investigates self-maps T : X ? X which satisfy a distance constraint in a metric space... more This paper investigates self-maps T : X ? X which satisfy a distance constraint in a metric space with mixed point-dependent non-expansive properties or, in particular, contractive ones, and potentially expansive properties related to some distance threshold. The above mentioned constraint is feasible in certain real-world problems of usefulness, for instance, when discussing ultimate boundedness in dynamic systems which guarantees Lyapunov stability. This fact makes the proposed analysis to be potentially useful to investigate global stability properties in dynamic systems in the potential presence of some locally unstable equilibrium points. The results can be applied to stability problems of dynamics systems and circuit theory as the given examples suggest.

Research paper thumbnail of On the asymptotic hyperstability of switched systems under integral-type feedback regulation Popovian constraints

IMA Journal of Mathematical Control and Information, 2014

Asymptotic hyperstability is achievable under certain switching laws if at least one of the feedf... more Asymptotic hyperstability is achievable under certain switching laws if at least one of the feedforward parameterization: 1) possesses a strictly positive real transfer function, 2) a minimum residence time interval is respected for each activation time interval of such a parameterization, and 3) a maximum allowable residence time interval is guaranteed for all active parameterization which is not positive real.

Research paper thumbnail of Robust Sliding Control of SEIR Epidemic Models

Mathematical Problems in Engineering, 2014

This paper is aimed at designing a robust vaccination strategy capable of eradicating an infectio... more This paper is aimed at designing a robust vaccination strategy capable of eradicating an infectious disease from a population regardless of the potential uncertainty in the parameters defining the disease. For this purpose, a control theoretic approach based on a sliding-mode control law is used. Initially, the controller is designed assuming certain knowledge of an upper-bound of the uncertainty signal. Afterwards, this condition is removed while an adaptive sliding control system is designed. The closed-loop properties are proved mathematically in the nonadaptive and adaptive cases. Furthermore, the usual sign function appearing in the sliding-mode control is substituted by the saturation function in order to prevent chattering. In addition, the properties achieved by the closed-loop system under this variation are also stated and proved analytically. The closed-loop system is able to attain the control objective regardless of the parametric uncertainties of the model and the lack of a priori knowledge on the system.

Research paper thumbnail of Partial stability of controlled SEIR epidemic models

This paper proposes to use the concept of partial stability instead of that of global stability t... more This paper proposes to use the concept of partial stability instead of that of global stability to analyze the dynamic behavior of epidemic models. The rationale behind this is that it is only needed, from a practical point of view, to ensure the boundedness of the infectious and infected subpopulations in order to get the disease under control. Thus, the partial stability of a controlled SEIR epidemic model is studied in the vaccination-free case. It will be proved that the infectious and infected subpopulations may still be bounded when the total population increases and global stability is not achieved. In addition, a feedback-based vaccination policy is designed based on the concept of partial stability of the closed-loop system. Some numerical simulations illustrating the usefulness of the designed control law along with a comparison with previous vaccination laws complete the paper.

Research paper thumbnail of A pole-placement based scheme for robustly stable adaptive control of continuous linear systems with multiestimation

Proceedings of the 20th IEEE International Symposium on Intelligent Control, ISIC '05 and the 13th Mediterranean Conference on Control and Automation, MED '05, 2005

This paper deals with the pole-placement type robust adaptive control of continuous linear system... more This paper deals with the pole-placement type robust adaptive control of continuous linear systems in the presence of bounded noise and a common class of unmodeled dynamics with the use of multiple estimation schemes working in parallel. The multiestimation scheme consisting of the above set of various single estimation schemes is a tool used to minimize the plant identification error by building an estimate which is a convex combination of the estimates at all time. The weighting functions of the individual estimates are provided at each time by a suboptimization scheme for a quadratic loss function of a possibly filtered tracking error and / or control input. The robust stability of the overall adaptive scheme is ensured by an adaptation relative dead zone which takes into account the contribution of the unmodeled dynamics and bounded noise. The basic results are derived for two different estimation strategies which have either a shared regressor with the plant or individual regressors for the input contribution and its relevant time-derivatives. In this second case, the plant input is obtained through a similar convex combination rule as the one used for the estimators in the first approach.

Research paper thumbnail of Control adaptable discreto con esquema de multiestimación en paralelo con incorporación de técnicas de supervisión e inteligencia artificial. Aplicaciones al control de manipuladores robóticos

Research paper thumbnail of Control adaptable discreto con esquemas de multiestimación en paralelo con incorporación de técnicas de supervisión e inteligencia artificial. Aplicaciones al control de manipuladores robóticos

Research paper thumbnail of A time-varying SIS epidemic model with incidence rate depending on the susceptible and infective populations with eventual impulsive effects

Applied Mathematics and Computation, 2013

This paper is concerned with a SIS (susceptible, infected and susceptible populations) propagatio... more This paper is concerned with a SIS (susceptible, infected and susceptible populations) propagation disease model with a nonlinear incidence rate and eventual impulsive (non-necessarily being simultaneous) culling of both populations. The disease transmission does not necessarily take into account the total population as a normalizing effect. In this sense, the considered model is a mixed pseudo-mass. The positivity, stability of both the impulse-free and impulsive under pulse culling variants of the model are investigated in this paper.

Research paper thumbnail of Multi-Model Smith Predictor Based Control of Multivariable Systems with Uncertain Bounded External Delays

IEEE Latin America Transactions, 2009

One of the drawbacks of the Smith Predictor (SP) to control systems with external point delays is... more One of the drawbacks of the Smith Predictor (SP) to control systems with external point delays is that its performance is strongly influenced by the knowledge of the time delay of the plant. Hence, as the mismatch between the actual delay of the plant and the nominal one used in the control structure increases, the closed-loop performance degrades accordingly, even potentially causing instability. This effect is particularly important when dealing with multivariable systems, where there is a coupling between input and output variables. In this paper, an intelligent frame to reduce the a priori knowledge of the plant delays required in the design of SP controllers for multivariable systems is proposed. The intelligent frame is composed of a set of different plant delay models running in parallel along with a high level supervision algorithm which selects the one that best describes the actual delay of the plant at each time interval to be used for control purposes. In this way, the designer can design the control of the system based on its delay-free part while the appropriate tuning of the delay of the Smith Predictor is performed by the intelligent supervisor. As a consequence, like simulation examples show, the closed-loop performance of the system is improved without the a priori requirement of an accurate knowledge of the value for the time delay.

Research paper thumbnail of Inventory control of supply chains: Mitigating the bullwhip effect by centralized and decentralized Internal Model Control approaches

European Journal of Operational Research, 2013

In this paper, a two-degrees-of-freedom Internal Model Control structure is incorporated in produ... more In this paper, a two-degrees-of-freedom Internal Model Control structure is incorporated in production inventory control for a supply chain system. This scheme presents an intuitive and simple parametrization of controllers, where inventory target tracking and disturbance (demand) rejection in the inventory level problems are treated separately. Moreover, considering that the lead times are known, this scheme presents a perfect compensation of the delay making the stabilization problem easier to handle. This control structure is formulated for a serial supply chain in two ways (by using a centralized and a decentralized control approach). The behavior of these inventory control strategies is analyzed in the entire supply chain. Analytical tuning rules for bullwhip effect avoidance are developed for both strategies. The results of controller evaluations demonstrate that centralized control approach enhances the behavior with respect to the inventory target tracking, demand rejection and bullwhip effect in the supply chain systems.

Research paper thumbnail of Asymptotically non-expansive self-maps and global stability with ultimate boundedness of dynamic systems

Applied Mathematics and Computation, 2013

This paper investigates self-maps T : X ? X which satisfy a distance constraint in a metric space... more This paper investigates self-maps T : X ? X which satisfy a distance constraint in a metric space with mixed point-dependent non-expansive properties or, in particular, contractive ones, and potentially expansive properties related to some distance threshold. The above mentioned constraint is feasible in certain real-world problems of usefulness, for instance, when discussing ultimate boundedness in dynamic systems which guarantees Lyapunov stability. This fact makes the proposed analysis to be potentially useful to investigate global stability properties in dynamic systems in the potential presence of some locally unstable equilibrium points. The results can be applied to stability problems of dynamics systems and circuit theory as the given examples suggest.