Identification of dynamic systems with position dependent load parameters

Cascaded control is still the most common and convenient structure in standard commercial drives. The most convenient tuning method is to apply calculation rules on an offline identified frequency response of the open-loop system. Obviously, this standard approach is only valid for linear time-invariant systems. However, the mechanical dynamics of modern machines very often depend on the angular position of the driven axis. Consequently, the system is time-variant and linearisation is needed to obtain an open-loop frequency response. In this paper, a system identification approach based on this linearisation is presented for dynamic systems with variable load torque and variable load inertia. The feasibility of this approach is validated with measurements on an industrial case.