Raffaello D'Andrea

Control of rotating stall in a low-speed axial flow compressor using pulsed air injection: modeling, simulations, and experimental validation

Previous results in the use of pulsed air injection for active control of rotating stall have suggested that air injectors have the effect of shifting the steady state compressor characteristic. In this paper we analyze the effect of a compressor characteristic actuation scheme for the three state Moore Greitzer compression system model. It is shown that closed loop feedback based on the square magnitude of the first rotating stall mode can be used to decrease the hysteresis region associated with the transition from unstalled to stalled and back to unstalled operation. The compressor characteristic shifting idea is then applied to a higher fidelity distributed model in which the characteristic shifting has phase content in addition to the magnitude content captured by the three state model. The optimal phasing of the air injection relative to the sensed position of the stall cell is determined via simulation and the results found to agree with those obtained via an experimental parametric study on the Caltech low-speed axial flow compressor.

Control of spatially varying distributed systems

Considers control design for distributed systems, where the controller is to adopt and preserve the spatial structure of the system. Specifically systems that vary spatially are considered; namely those that are not shift invariant with respect to spatial variables. Operator theoretic tools for working with these systems are developed, and lead to convex conditions for analysis and synthesis with respect to the /spl Lscr//sub 2/-induced norm.

Behavioral approach to robustness analysis

This paper introduces a general and powerful framework for modeling and analysis of uncertain systems. One immediate concrete result of this work is a practical method for computing robust performance in the presence of norm-bounded perturbations and both norm-bounded and white-noise disturbances.

Interconnection of uncertain behavioral systems for robust control

This paper attempts to relate robust control and behavioral frameworks by incorporating structured uncertainty into the description of behavioral systems. Behavioral equations are expressed as linear fractional transformations (LFTs) on an uncertainty structure, and a method of interconnection is outlined. A method for obtaining input-output maps from LFT representations of behavioral systems is also presented. This extension of the behavioral framework is compatible with existing robust control methods, such as /spl mu/ analysis, which can be used to provide robustness test in behaviors. A simple example is presented that illustrates some of the issues which arise in this extension.<<ETX>>

Minimality, controllability and observability for uncertain systems

A complete generalization of the notions of minimality, controllability and observability is presented for uncertain systems modelled by linear fractional transformations on structured operators. Both an algebraic perspective and a geometric perspective are given. The algebraic results include necessary and sufficient linear matrix inequality conditions for reducibility, and the development of structured controllability and observability matrices. The geometric approach involves a decomposition of the system variable space into reachable and unobservable subspaces. Both approaches lead to Kalman-like decomposition structures for uncertain systems.

A State-Space Theory of Uncertain Systems

Abstract This paper presents a tutorial summarizing recent work on generalizing standard state-space results such as stability and performance analysis, realization theory, stability and stabilization, and H ∞ optimal control to uncertain systems described by Linear Fractional Transformations (LFTs)

H/sub /spl infin// optimization with spatial constraints

A generalized H/sub /spl infin// synthesis problem where nonEuclidian spatial norms on the disturbances and output error are used is posed and solved. The solution takes the form of a linear matrix inequality. Some problems which fall into this class are presented. In particular, solutions are presented to two problems: a variant of H/sub /spl infin// synthesis where norm constraints on each component of the disturbance can be imposed, and synthesis for a certain class of robust performance problems.

Simplification of spatially distributed systems

A technique for the simplification of spatially distributed systems is presented. This technique relies on linear matrix inequality (LMI) based reduction results originally developed for the simplification of uncertain and multi-dimensional systems. The original results are applicable to systems that can be modelled by linear fractional transformations (LFTs) on structured operator sets whose elements are assumed to be temporal variables. In the paper, the original LFT results are extended to systems written as LFTs on spatial variables as well as on temporal variables. The main technical difference in the derivation of the new reduction results is a relaxation of standard causality requirements (or equivalently stability requirements), which in turn leads to a relaxation of the constraints to the relevant LMI solutions.

Active control of rotating stall using pulsed-air injection: a parametric study on a low-speed axial flow compressor

This paper presents preliminary results on the use of low flow, high momentum, pulsed air injectors to control the onset of stall in a low-speed, axial flow compressor. By measuring the unsteady pressures in front of the rotor, the controller determines the magnitude and phase of a stall cell and controls the injection of air in front of the rotor face. Initial experimental results have verified that controller slightly extends the stall point of the compressor and virtually eliminates the hysteresis loop normally associated with stall. An explanation of this effect is proposed based on the quasi-steady effects of air injection on the compressor characteristic curve.

Full information and full control in a behavioral context

In this paper, the concepts of full information (FI) and full control (FC), which arise in standard H/sub /spl infin// theory, are extended to the behavioral framework. The H/sub /spl infin// optimal interconnection problem formulation is outlined and the solution presented. The behavioral versions of the FI and FC problems are introduced, followed by connections with the input/output versions of the FI and FC problems and the associated Riccati equations. An illustrative example is presented.