Design of feedback control systems for stable plants with saturating actuators

A systematic control design methodology is introduced for multi-input/multi-output stable open loop plants with multiple saturations. This new methodology is a substantial improvement over previous heuristic single-input/single-output approaches. The idea is to introduce a supervisor loop so that when the references and/or disturbances are sufficiently small, the control system operates linearly as designed. For signals large enough to cause saturations, the control law is modified in such a way as to ensure stability and to preserve, to the extent possible, the behavior of the linear control design. Key benefits of the methodology are: the modified compensator never produces saturating control signals, integrators and/or slow dynamics in the compensator never windup, the directional properties of the controls are maintained, and the closed loop system has certain guaranteed stability properties. The advantages of the new design methodology are illustrated in the simulation of an academic example and the simulation of the multivariable longitudinal control of a modified model of the F-8 aircraft

Design of feedback control systems for unstable plants with saturating actuators

A new control design methodology is introduced for multi-input/multi-output systems with unstable open loop plants and saturating actuators. A control system is designed using well known linear control theory techniques and then a reference prefilter is introduced so that when the references are sufficiently small, the control system operates linearly as designated. For signals large enough to cause saturations, the control law is modified in such a way to ensure stability and to preserve, to the extent possible, the behavior of the linear control design. Key benefits of this methodology are: the modified feedback system never produces saturating control signals, integrators and/or slow dynamics in the compensator never windup, the directionaL properties of the controls are maintained, and the closed loop system has certain guaranteed stability properties. The advantages of the new design methodology are illustrated in the simulation of an approximation of the AFTI-16 (Advanced Fighter Technology Integration) aircraft multivariable longitudinal dynamics

A method for designing robust multivariable feedback systems

A new methodology is developed for the synthesis of linear, time-invariant (LTI) controllers for multivariable LTI systems. The aim is to achieve stability and performance robustness of the feedback system in the presence of multiple unstructured uncertainty blocks; i.e., to satisfy a frequency-domain inequality in terms of the structured singular value. The design technique is referred to as the Causality Recovery Methodology (CRM). Starting with an initial (nominally) stabilizing compensator, the CRM produces a closed-loop system whose performance-robustness is at least as good as, and hopefully superior to, that of the original design. The robustness improvement is obtained by solving an infinite-dimensional, convex optimization program. A finite-dimensional implementation of the CRM was developed, and it was applied to a multivariate design example

Performance and robustness analysis for structured uncertainty

This paper introduces a nonconservative measure of performance for linear feedback systems in the face of structured uncertainty. This measure is based on a new matrix function, which we call the Structured Singular Value

A General Statement of Structured Singular Value Concepts

Some key concepts of strucred singular value theory for the stability and performance-robustness analysis of linear time-invariant multivariable systems are stated. Using a set-invariance principle, the theory is then generalized to allow for nonlinear and/or time-varying nominal systems and uncertainties. The general theory is then re-specialized to the case of nominally linear time-invariant systems subject to L2-induced-norm bounded uncertainties

Sufficient conditions for robust performance of adaptive controllers with general uncertainty structure

Sufficient conditions are given under which an adaptive control system is robustly stable and achieves a guaranteed robust asymptotic performance level equal to that of the robust controller given perfect parameter information. The conditions are general in several respects. For example, structured non-parametric uncertainty (e.g. block diagonal) is allowed, as well as exogenous noise inputs. In addition, the structure of the parametric uncertainty is very general, and even allows for parameters which scale the uncertainty magnitudes. This allows one to identify the size of the non-parametric uncertainty and to schedule the controller based on this size. Finally, the robust gain scheduled controller is largely unrestricted. Identification mechanisms which are proven to satisfy the sufficient conditions are not given here and, for the general problem, have not yet been developed. However, an example of such a mechanism for a subclass of systems does exist and is referenced. For the general problem, this paper provides properties to be sought in the development of robust identification laws for robust adaptive control.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30184/1/0000569.pd

Performance and robustness analysis for structured uncertainty

This paper introduces a nonconservative measure of performance for linear feedback systems in the face of structured uncertainty. This measure is based on a new matrix function, which we call the Structured Singular Value

Estimating process capability index Cpm using a bootstrap sequential sampling procedure

Construction of a confidence interval for process capability index CPM is often based on a normal approximation with fixed sample size. In this article, we describe a different approach in constructing a fixed-width confidence interval for process capability index CPM with a preassigned accuracy by using a combination of bootstrap and sequential sampling schemes. The optimal sample size required to achieve a preassigned confidence level is obtained using both two-stage and modified two-stage sequential procedures. The procedure developed is also validated using an extensive simulation study.<br /

The asteroseismic surface effect from a grid of 3D convection simulations - I. Frequency shifts from convective expansion of stellar atmospheres

We analyse the effect on adiabatic stellar oscillation frequencies of replacing the near-surface layers in 1D stellar structure models with averaged 3D stellar surface convection simulations. The main difference is an expansion of the atmosphere by 3D convection, expected to explain a major part of the asteroseismic surface effect, a systematic overestimation of p-mode frequencies due to inadequate surface physics.We employ pairs of 1D stellar envelope models and 3D simulations from a previous calibration of the mixing-length parameter, α. That calibration constitutes the hitherto most consistent matching of 1D models to 3D simulations, ensuring that their differences are not spurious, but entirely due to the 3D nature of convection. The resulting frequency shift is identified as the structural part of the surface effect. The important, typically non-adiabatic, modal components of the surface effect are not included in this analysis, but relegated to future papers. Evaluating the structural surface effect at the frequency of maximum mode amplitude, υmax, we find shifts from δυ = -0.8 μHz for giants at log g = 2.2 to -35 μHz for a (Teff = 6901 K, log g = 4.29) dwarf. The fractional effect δυ(υmax )/υmax, ranges from -0.1 per cent for a cool dwarf (4185 K, 4.74) to -6 per cent for a warm giant (4962 K, 2.20)RT acknowledges funding from NASA grant NNX15AB24G. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant DNRF106)

The prevalence of mental health problems in sub-saharan adolescents : a systematic review

Background and purpose Most research regarding child and adolescent mental health prevention and promotion in low-and middle-income countries is undertaken in high-income countries. This systematic review set out to synthesise findings from epidemiological studies, published between 2008 and 2020, documenting the prevalence of mental health problems in adolescents from across sub-Saharan Africa. Methods A systematic search of multiple databases (MEDLINE, PsycINFO, Scopus) and Google Scholar was conducted guided by the Joanna Briggs Institute (JBI) Reviewer's manual for systematic reviews of observational epidemiological studies. Studies included reported prevalence outcomes for adolescents aged 10-19 using either clinical interviews or standardized questionnaires to assess psychopathology. Clinical samples were excluded. Results The search yielded 1 549 records of which 316 studies were assessed for eligibility and 51 met the inclusion criteria. We present a qualitative synthesis of 37 of these 51 included articles. The other 14 studies reporting prevalence rates for adolescents living with HIV are published elsewhere. The prevalence of depression, anxiety disorders, emotional and behavioural difficulties, posttraumatic stress and suicidal behaviour in the general adolescent population and selected at-risk groups in 16 sub-Saharan countries (with a total population of 97 616 adolescents) are reported.Hochschule für Angewandte Wissenschaften HamburgPeerReviewe