This paper is devoted to design of stochastic robust anisotropy-based reduced-order controller for longitudinal flight control in landing approach under the influence of both deterministic and stochastic external disturbances. The control aims at disturbance attenuation and stabilizing aircraft longitudinal motion along some desired glidepath. The controller design procedure consists of two steps. At first, the full-order optimal controller is obtained as the solution to normalized anisotropy-based stochastic Η∞ optimization problem. Then, the optimal controller is reduced via a truncation-like technique. The results of comparison of reduced-order anisotropic controller with LQG and Η∞ ones on the base of closed-loop system simulation are presented.
In this paper, an improvement in Pade approximation is proposed to reduce the order of a linear-time-invariant higher order stable system, using the Hermite-Biehler stability theorem. Two free parameters are introduced in the denominator polynomial of the reduced model. It will be shown that for any positive values of these two parameters, the resulting reduced model will be stable. The numerator polynomial and these two parameters are obtained by matching time moments. In this proposed algorithm, the reduced model matches (r + 2) time moments exactly while (r + 3)-th moment is matched approximately. The proposed method is illustrated by two numerical examples.
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The text covers an in-depth study on the order of the compensator applied in a feedback system for stabilization of the linear, time-invariant, n-th order, multivariable plant. It is shown that all such compensators evolve from the n-th order structure depicted in two forms in Fig. 2 (dotted lines). Presentation includes the so-called reduced and subreduced order compensators and the case of a static output feedback, i.e. the compensator of order zero. All theoretical considerations are supported by examples, in which various types of compensators are synthesized.
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