A fuzzy disturbance observer and its application to control

In this paper, a fuzzy disturbance observer (FDO) is developed and its application to the control of a nonlinear system under the internal and external disturbances is presented. To construct the FDO, two parameter tuning methods are proposed and shown to be useful in adjusting the parameters of the FDO. The first tuning method employes the disturbance observation error to guarantee that the FDO monitors the unknown disturbance. The next one enlarges the concept of error and introduces augmented error to guarantee that the FDO monitors the disturbance and the control objective is achieved. In addition, the relationships between the suggested FDO-based control and the conventional adaptive fuzzy controls reported in the previous literatures are discussed and it is shown in a rigorous manner that the disturbance observation error or the augmented error converges to a region of which size can be kept arbitrarily small. Finally, some examples and computer simulation results are presented to illustrate the effectiveness and the applicability of the FDO.