This paper investigates the use of generalized sampled-data hold functions (GSHF) in the control of linear time-invariant systems. The idea of GSHF is to periodically sample the output of the system, and generate the control by means of a hold function applied to the resulting sequence. The hold function is chosen based on the dynamics of the system to be controlled. This method appears to have several advantages over dynamic controllers: it has the efficacy of state feedback without the requirement of state estimation; it provides the control system designer with substantially more freedom; and it requires few on-line computations. This paper focuses on four questions: pole assignment, specific behavior, noise sensitivity, and robustness. Among the problems solved are: simultaneous arbitrary pole assignment for a finite number of systems by a single GSHF controller, exact model matching, decoupling, and optimal noise rejection. Examples are given.

Control of linear systems using generalized sampled-data hold functions

Nondifferentiable optimization algorithm for designing control systems having singular value inequalities

This paper presents a comprehensive study of the ac stability of high power factor rectifiers, proposing a new stability criterion to assess this condition under constant power load dynamics. Specifically, based on the multivariable generalized Nyquist stability criterion developed by MacFarlane and Postlethwaite, this paper shows how the fundamental stability problem at such ac interface is indeed reduced to a single-input single-output (SISO) case. It is shown that the ac stability is fully determined by the SISO return-ratio of the d-d channel—or the power transfer channel of the desired d-q frame alignment; that is, the stability is determined by the d-d channel input and output impedances. Correspondingly, it is shown that the q-q channel trajectory on the complex plane is such that it cannot encircle the critical point (−1+j0) and therefore be the cause of instability. The ac stability at the input terminals of the rectifier can then be fully assessed using the standard SISO Nyquist stability theorem, in sheer duality of Middlebrook's criterion for dc-dc converters. Simulation results are used to verify and appraise the implications of the proposed ac system stability criterion.

On the Ac stability of high power factor three-phase rectifiers

Dynamic inversion, or feedback linearization theory, represents a commonly used nonlinear control method for designing aircraft control laws. This method has the ability to control a highly nonlinear plant but suffers from the lack of guaranteed robustness. The stability and flying qualities robustness of a dynamic inversion based control law, designed for a prototype aircraft, to uncertain aerodynamic parameters is analyzed. The results indicate that the pitch plane stability and flying qualities are robust to parameter uncertainties, but the lateral directional flying qualities are sensitive to uncertain stability derivatives.

Stability and flying qualities robustness of a dynamic inversion aircraft control law

The paper describes the theory and application fo a multi-input/multi-output self-tuning regulator where the control objective is the assignment of the closed-loop pole set to prespecified locations. The key theoretical result is that the algorithm has the so-called ‘self-tuning’ property. From a practical viewpoint the pole-assignment concept leads to direct digital controllers which are more robust than self tuners based on optimal control synthesis methods.

Harry Nyquist

Papers

Frequency-response methods in control systems