Internal Model Unit Research Articles

Energy‐based output regulation for stochastic port‐Hamiltonian systems

AbstractThis article investigates the output regulation for stochastic port‐Hamiltonian systems (SPHSs) subject to sinusoidal disturbances. An energy‐based regulation scheme with an internal model unit is proposed by exploiting the stochastic Hamiltonian structure, which drives the tracking error to the origin while maintaining asymptotical stability in probability of the closed‐loop system. An energy‐based robust regulation scheme as well as an alternative condition is then developed without solving Hamilton–Jacobi–Issacs inequalities. The proposed regulators preserve the stochastic Hamiltonian structure of the disturbed SPHS by coordinate transformation. Hence the output regulation problems fall into the stabilization framework for SPHSs and there is no need to solve regulator equations. These results cover the stabilization of SPHSs and the output regulation of deterministic port‐Hamiltonian systems. Simulations on an inverted pendulum show the effectiveness of the proposed methods.

Distributed Model Reference Adaptive Optimization of Disturbed Multiagent Systems With Intermittent Communications.

This article pays close attention to a distributed optimization problem for multiagent systems subject to exogenous disturbances. A novel distributed model reference adaptive control (D-MRAC) scheme is proposed that no explicit disturbance observer or internal model unit is involved, which not only enhances robustness but also improves transient performance. In contrast to the continuous communication that is often assumed in the existing distributed optimization works, the new method allows for more realistic scenarios in which the agents communicate with each other at discrete-time instants. It is shown by Lyapunov analysis that the concerned distributed optimization problem can be solved by the proposed D-MRAC scheme as long as the communication interval is smaller than a given threshold, which can be calculated by following the steps given in this article. Numerical simulations have shown the effectiveness of the presented method.

Implementing PRED Subroutine of NONMEM for Versatile Pharmacokinetic Analysis Using Fast Inversion of Laplace Transform (FILT).

In pharmacokinetic (PK) analysis, conventional models are described by ordinary differential equations (ODE) that are generally solved in their Laplace transformed forms. The solution in the Laplace transformed forms is inverse Laplace transformed to derive an analytical solution. However, inverse Laplace transform is often mathematically difficult. Consequently, numerical inverse Laplace transform methods have been developed. In this study, we focus on extending the modeling functions of Nonlinear Mixed Effect Model (NONMEM), a standard software for PK and population pharmacokinetic (PPK) analyses, by adding the Fast Inversion of Laplace Transform (FILT) method, one of the representative numerical inverse Laplace transform methods. We implemented PREDFILT, a specialized PRED subroutine, which functions as an internal model unit in NONMEM to enable versatile FILT analysis with second-order precision. The calculation results of the compartment models and a dispersion model are in good agreement with the ordinary analytical solutions and theoretical values. Therefore, PREDFILT ensures enhanced flexibility in PK or PPK analyses under NONMEM environments.

Output regulation by postprocessing internal models for a class of multivariable nonlinear systems

SummaryIn this paper we propose a new design paradigm, which employs a postprocessing internal model unit, to approach the problem of output regulation for a class of multivariable minimum‐phase nonlinear systems possessing a partial normal form. Contrary to previous approaches, the proposed regulator handles control inputs of dimension larger than the number of regulated variables, provided that a controllability assumption holds, and can employ additional measurements that need not to vanish at the ideal error‐zeroing steady state, but that can be useful for stabilization purposes or to fulfill the minimum‐phase requirement. Conditions for practical and asymptotic output regulation are given, underlying how in postprocessing schemes the design of internal models is necessarily intertwined with that of the stabilizer.

Robust stabilizer design for linear time-varying internal model based output regulation and its application to an electrohydraulic system

This paper focuses on the design of a low order robust stabilizer for the tracking/disturbance rejection problem based on the internal model principle in the time-varying setting and its application to the hydraulic pressure tracking with varying frequency. The problem of this kind known as output regulation generally consists of two major parts: internal model unit construction and stabilizer design. While the construction of the time-varying internal model unit is non-trivial by itself and a very recent research outcome enables its synthesis for a class of linear time-varying systems, the effective stabilization of the augmented system (internal model unit and plant) for practical applications remains a challenge. This is due to the need to stabilize the high order time-varying augmented system using a low order stabilizer in a robust fashion and with desirable transient performance. While directly applying the stabilization approaches for a general LTV system will result in a high order stabilizer, a new method is proposed in this paper that overcomes this bottleneck by taking advantage of the unique structure of the internal model based control system. Instead of using a dynamic stabilizer with high order, this approach uses a sequence of time-varying gains that are directly injected into the internal model unit. A critical issue addressed is how to avoid the non-convex optimization associated with the time-varying gain synthesis and then convert the stabilizer design into a series of Linear Matrix Inequalities (LMIs). The proposed control approach is then demonstrated on an electrohydraulic system.

The formation and performance of medical humanities by interns in a clinical setting

ObjectivesThere were two aims of this study: first, we attempted to identify the medical humanities performed by interns in the clinical ward; second, we wanted to explore the ways that interns learn medical humanities. Materials and MethodsThis research was carried out in a general internal medicine model unit of a medical center in southern Taiwan. Researchers conducted field work by participant observation in the ward for 9 months from December 2008 to May 2009, and from November 2009 to January 2010. Eight interns were enrolled in this study. Humanistic behaviors performed by the interns who were investigated during the course of their medical activities were recorded in field records. After participant observation, five interns were interviewed to collect information on their learning processes related to medical humanities. The field records and interview transcriptions were coded according to categories of medical professionalism defined in this study. ResultsFour major characteristics of medical humanities were observed from the field work: primacy of patient welfare, patient autonomy, social justice, and sincerity. The most common humanistic practices performed by the interns included converting medical knowledge into lay language when communicating with the patient’s family, closing the bedside curtain for privacy and arranging social worker consultations to help patients. Three learning models were also identified that were associated with the performance of humanistic practices observed in the field. Interns may learn medical humanities through learning by doing, a teaching-learning model, informal peer learning, or a combination of these. ConclusionThis study confirmed that sincerity is a characteristic of medical professionalism and medical humanities. Participant observation can be used as an ideal tool for identifying humanistic medical practices in daily clinical settings, and an interview can become a supplemental method to validate what has been observed.

Trajectory tracking and disturbance rejection for linear time-varying systems: Input/output representation

This paper considers the problem of asymptotic trajectory tracking and/or disturbance rejection for linear time-varying systems via input/output representation. Inspired by the structure of repetitive control, a novel feedback mechanism is proposed based on which the necessary and sufficient condition for the problem is derived. This condition is a generalization to the time-varying case of the result in time-invariant setting. Based on the complete knowledge of the plant model, a design is provided and it is applicable to repetitive control for time-varying plants. An important feature of the proposed approach is that a systematic way of constructing time-varying internal model unit is provided.

Regulation and Input Disturbance Suppression for Port-Controlled Hamiltonian Systems

In this paper the output feedback regulation problem for port-controlled Hamiltonian systems (PCHS) is addressed. Following the nonlinear output regulation theory, the regulator which solves the problem is given by a parallel connection of two subcontrollers: an internal model unit and a regulator to stabilize the extended system composed by the plant and the internal model unit. The main idea is to use the PCHS theory in order to design that stabilizer controller: as in many cases the plant to be addressed is indeed a mechanical/electric system, and it is very easy to think about it as a PCHS, the paper shows the conditions to fulfill in order to design the internal model unit as a PCHS, allowing to use the powerful energy-shaping theory in order to stabilize the extended system. Moreover the same techniques are used to design an internal model based controller able to globally solve a problem of input disturbance suppression

A Note on Disturbance Suppression for Hamiltonian Systems by State Feedback

The problem of disturbance rejection for a class of Hamiltonian systems is addressed and solved. It is shown that the state feedback regulator achieving asymptotic suppression of matched disturbances can be designed in two stages: in the former a state feedback stabilizer is constructed and in the latter the internal model unit is built, i.e. a sort of separation result holds. Finally, the application of the theory to the problem of disturbance suppression in a magnetic levitation system is presented