Comparison of two approaches to a positional servo control

The paper deals with comparison of a filtered disturbance observer based PID control (DO FPID) with different realizations of a two-degree-of-freedom (2DOF) PID control. It shows that whereas in terms of IAE (Integral of absolute error) of the setpoint and disturbance step responses, both solutions may yield an equivalent closed loop dynamics, the DO FPID control guarantees a much better quantization noise attenuation [1]-[3]. It is shown that this property may be used in such a way that whereas the torque ripple of both alternatives evaluated by a modified total variance measure takes equivalent values, IAE values of the loop with the DO-FPID will significantly decrease.