Comparing integral disturbance observer based controllers with input and output disturbance compensation

Proportional-integral (PI) controllers represent huge majority of all controllers applied in practice. Despite their broad use, different alternative solutions have been developed based on reconstruction and compensation of input, or output disturbances. Whereas a compensation of output disturbances reconstructed by a parallel plant model represents a key element of the well known internal model control (IMC) used frequently in process control, here it will be applied also in a structure with a reference model and a stabilizing controller. A reconstruction and compensation of input (load) disturbances is frequently applied in the motion control area. This paper deals with a comparison of these two basic approaches combined with a stabilizing P controller with an IMC and demonstrates their pros and cons by controlling simple thermo-optical plant.