Analogue realizations of fractional-order controllers

An approach to the design of analogue circuits, implementing fractional-order controllers, is presented. The suggested approach is based on the use of continued fraction expansions; in the case of negative coefficients in a continued fraction expansion, the use of negative impedance converters is proposed. Several possible methods for obtaining suitable rational appromixations and continued fraction expansions are discussed. An example of realization of a fractional-order I(<)lambda> controller is presented and illustrated by obtained measurements. The suggested approach can be used for the control of very fast processes, where the use of digital controllers is difficult or impossible.