Affine linear parameter-varying embedding of non-linear models with improved accuracy and minimal overbounding

In this study, automated generation of linear parameter-varying (LPV) state-space models to embed the dynamical behaviour of non-linear systems is considered, focusing on the trade-off between scheduling complexity and model accuracy and the minimisation of the conservativeness of the resulting embedding. The LPV state-space model is synthesised with affine scheduling dependency, while the scheduling variables themselves are non-linear functions of the state and input variables of the original system. The method allows to generate complete or approximative embedding of the non-linear system model and also it can be used to minimise the complexity of existing LPV embeddings. The capabilities of the method are demonstrated on simulation examples and also in an empirical case study where the first-principle motion model of a three degrees of freedom (3DOF) control moment gyroscope is converted by the proposed method to an LPV model with low scheduling complexity. Using the resulting model, a gain-scheduled controller is designed and applied on the gyroscope, demonstrating the efficiency of the developed approach

An Overview on Hybrid Integrator-Gain Systems with applications to Wafer Scanners

ybrid integrator-gain systems (HIGS) are nonlinear control elements that switch between simple integrator dynamics and gain characteristics. Switching is done in a waythat guarantees sign-equivalence of the integrator’s input-output pair, thereby enabling phase advantages over linear integrators as seen through describing function analysis. This paper provides an overview of the state of the art in HIGS controlled systems analysis and design with applications to wafer scanners. Index Terms—hybrid integrator-gain systems, motion systems, nonlinear PID-control, reset control.Hybrid integrator-gain systems (HIGS) are non- linear control elements that switch between simple integrator dynamics and gain characteristics. Switching is done in a way that guarantees sign-equivalence of the integrator's input-output pair, thereby enabling phase advantages over linear integrators as seen through describing function analysis. This paper provides an overview of the state of the art in HIGS controlled systems analysis and design with applications to wafer scanners.</p

Hybrid integrator-gain system for active vibration isolation with improved transient response

In this paper a linear bandpass filter is compared to a hybrid integrator-gain based bandpass filter regarding its usefulness in active vibration isolation. Vibration isolation refers to a form of skyhook damping in which a velocity output signal from a system having structural dynamics is fed back to a controller, the latter having bandpass characteristics. At those frequencies where the controller passes the input signal (after gain multiplication) a force proportional to velocity is obtained that can be used to provide active damping to the system, i.e., damping of one (or more) of its structural modes. Outside this frequency band the controller input signal is attenuated, which is often desirable in view of incorrect sensor information at low frequencies and/or to avoid amplification of high-frequency noise. In this context, the use of a hybrid integrator-gain system will be studied regarding its possible phase advantages compared to linear integrators. These advantages stem from the control design itself, in the sense that by design the control output force signal and the input velocity error signal have equal sign. In the context of vibration control, an enhanced transient (closed-loop) response is obtained, i.e., less overshoot and reduced settling times, but at the cost of increased rise times

Projection-based integrators for improved motion control: Formalization, well-posedness and stability of hybrid integrator-gain systems

In this paper we formally describe the hybrid integrator-gain system (HIGS), which is a nonlinear integrator designed to avoid the limitations typically associated with linear integrators. The HIGS keeps the sign of its input and output equal, thereby inducing less phase lag than a linear integrator, much like the famous Clegg integrator. The HIGS achieves the reduced phase lag by projection of the controller dynamics instead of using resets of the integrator state, which forms a potential benefit of this control element. To formally analyze HIGS-controlled systems, we present an appropriate mathematical framework for describing these novel systems. Based on this framework, HIGS-controlled systems are proven to be well-posed in the sense of existence and forward completeness of solutions. Moreover, we propose two approaches for analyzing (input-to-state) stability of the resulting nonlinear closed-loop systems: (i) circle-criterion-like conditions based on (measured) frequency response data, and (ii) LMI-based conditions exploiting a new construction of piecewise quadratic Lyapunov functions. A motion control example is used to illustrate the results

PGC-1α promotes recovery after acute kidney injury during systemic inflammation in mice

Sepsis-associated acute kidney injury (AKI) is a common and morbid condition that is distinguishable from typical ischemic renal injury by its paucity of tubular cell death. The mechanisms underlying renal dysfunction in individuals with sepsis-associated AKI are therefore less clear. Here we have shown that endotoxemia reduces oxygen delivery to the kidney, without changing tissue oxygen levels, suggesting reduced oxygen consumption by the kidney cells. Tubular mitochondria were swollen, and their function was impaired. Expression profiling showed that oxidative phosphorylation genes were selectively suppressed during sepsis-associated AKI and reactivated when global function was normalized. PPARγ coactivator–1α (PGC-1α), a major regulator of mitochondrial biogenesis and metabolism, not only followed this pattern but was proportionally suppressed with the degree of renal impairment. Furthermore, tubular cells had reduced PGC-1α expression and oxygen consumption in response to TNF-α; however, excess PGC-1α reversed the latter effect. Both global and tubule-specific PGC-1α–knockout mice had normal basal renal function but suffered persistent injury following endotoxemia. Our results demonstrate what we believe to be a novel mechanism for sepsis-associated AKI and suggest that PGC-1α induction may be necessary for recovery from this disorder, identifying a potential new target for future therapeutic studies