ABSTRACT
Two approaches are presented for modeling systems composed of electrical, mechanical, thermal, and hydraulic elements: describing the system elements and the topology of their connections, and deriving mathematical equations for the system. Several issues are considered that are important for feedback control: flexible structures, collocated and non-collocated control, sensor noise, and the effect of feedback on the output noise. An electrical dc motor is an electromechanical transducer. The loading for the disconnected ports must be preserved while disconnecting the feedback path for appropriate comparison of the system with and without feedback. Linear time-variable (LTV) links are described by linear equations whose coefficients explicitly depend on time. The phase shift for the passing signal in periodical LTV links depends on the phase of the incident signal. For small-signal deviations from the current value, nonlinear links can be seen as LTV links.
