1,721,002 research outputs found
Fractional order PI controllers for TCP packet flow ensuring given modulus margins
No full textAn Active Queue Management (AQM) robust control strategy for Traffic Control Protocol (TCP) data transfer is proposed. To this purpose, the TCP behaviour is first approximated by a second-order model with delayed input obtained from the linearization of an efficient and commonly used nonlinear fluid-based model. The adopted feedback control structure uses a fractional-order PI controller. To ensure the desired robustness, the parameter regions where such a controller guarantees a given modulus margin (inverse of the H∞ norm of the sensitivity function) are derived. An example commonly used in the literature is worked out to show that the suggested graphically-based design technique is simple to apply while it limits the effects of disturbances and of the unmodelled dynamics
A new method for the integer order approximation of fractional order models
No full textThis paper is concerned with the finite–dimensional approximation of a fractional–order system represented in state–space form. To this purpose, resort is made to the Oustaloup method for approximating a fractional–order integrator by a rational filter. The dimension of the resulting integer–order model can be reduced using an efficient algorithm for the minimization of the L2 norm of a weighted equation error. Two numerical examples are worked out to show how the desired approximation accuracy can be ensured
The Lepschy stability test and its application to fractional-order systems
Full text linkIt is shown how a stability test, alternative to the classical Routh test, can profitably be applied to check the presence of polynomial roots inside half-planes or even sectors of the complex plane. This result is obtained by exploiting the peculiar symmetries of the root locus in which the basic recursion of the test can be embedded. As is expected, the suggested approach proves useful for testing the stability of fractional-order systems. A pair of examples show how the method operates. It is believed that the suggested geometric approach can also be of some didactic value in introducing basic control-system tools to engineering students
On polynomial root distribution with respect to a sector
No full textThis paper extends previous results of the same authors on the determination of the polynomial root distribution with respect to a sector by means of elementary vector analysis. Specifically, it is shown how the overall phase variation of any real or complex polynomial along the radii of a sector accounts for the number of roots inside and outside the sector. The method applies to both symmetric and asymmetric sectors with respect to the real axis. Its practical application only requires plotting a Nyquist-like diagram (a hodograph). The procedure proves particularly useful in the stability analysis of fractional-order systems. A pair of examples is worked out to show how the method operates
A procedure to obtain the symbolic expression of input-output representations from a signal flow graph
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