Electrical servomotors are used in the so-called motion control systems in which position and/or speed are controlled. Starting with the input-output and the input-state-output mathematical models of a dc motor, this paper shows the simulation schematic of the system, which uses elementary blocks, and develops the mathematical representation and the simulation schematic for the case where the parameters of the model are affected by multiplicative uncertainties. The process of finding the general model for the dc motor is based on the linear-fractional transformation. Matlab is used for simulating the evolution of the motor’s angular velocity in time domain.

Keywords: Dc motor, Mathematical modelling, Uncertain systems, Linear fractional transform