Further Result on Reducing Disturbance-Compensation Error of Equivalent-Input-Disturbance Approach

This article carries out an inside observation of a disturbance-compensation error in the equivalent-input-disturbance (EID) approach and divides the causes of the compensation error into two types: disturbance- and state-estimation errors. A modified EID (MEID) approach precisely deals with each type separately. Considering that the disturbance-estimation error cannot be measured, we use a high-gain observer to ensure the rapid convergence of the disturbance-estimation error. Unlike the conventional EID approach, the MEID approach newly introduces a weighted output-estimation error, which is produced by a state observer, to compensate for the state-estimation error in a prescribed frequency range. A stability condition is devised for an MEID-based control system. The parameters of a filter and an observer are optimized simultaneously based on a time-domain performance index with a constraint in the frequency domain. An experimental comparison with other EID approaches demonstrates the superiority of the MEID approach.