Recent developments on the realization of fractance device

A detailed analysis of the recent developments on the realization of fractance device is presented. A fractance device which is used to exhibit fractional order impedance properties finds applications in many branches of science and engineering. Realization of fractance device is a challenging job for the people working in this area. A term fractional order element, constant phase element, fractor, fractance, fractional order differintegrator, fractional order differentiator can be used interchangeably. In general, a fractance device can be realized in two ways. One is using rational approximations and the other is using capacitor physical realization principle. In this paper, an attempt is made to summarize the recent developments on the realization of fractance device. The various mathematical approximations are studied and a comparative analysis is also performed using MATLAB. Fourth order approximation is selected for the realization. The passive and active networks synthesized are simulated using TINA software. Various physical realizations of fractance device, their advantages and disadvantages are mentioned. Experimental results coincide with simulated results.

An Integer-Order Transfer Function Estimation Algorithm for Fractional-Order PID Controllers

Fractional-order systems and controllers have been extensively used in many control applications to achieve robust modeling and controlling performance. To implement these systems, curve fitting based integer-order transfer function estimation techniques namely Oustaloup and Matsuda are most widely used. However, these methods are failed to achieve the best approximation due to the limitation of the desired frequency range. Thus, this article presents a simple curve fitting based integer-order transfer function estimation method for fractional-order differentiator/integrator using frequency response. The advantage of this technique is that it is simple and can fit the entire desired frequency range. Using the approach, an approximation table for fractional-order differentiator has also been obtained which can be used directly to obtain the approximation of fractional-order systems. A simulation study on fractional systems shows that the proposed approach produced better parameter approximation for the desired frequency as compared to Oustaloup, refined Oustaloup and Matsuda techniques.