Disturbance Observer Based Fault‐Tolerant Control of Switched Nonlinear Stochastic Systems With Unmatched Disturbance

ABSTRACT For switched fuzzy stochastic systems with multiple faults and unmatched disturbance, the issues of fault/disturbance estimation and fault‐tolerant anti‐disturbance control are considered. The dynamic observer is designed by introducing the output derivative information. In comparison to the existing results, the designed observer can reduce the effect of the actuator fault derivative, which is usually regarded as a disturbance, and obtain better estimation results, since the variation trend is included in the derivative of the output. The output‐based disturbance observer is designed. The mismatched disturbance is considered, which means that the disturbance cannot be compensated for completely. The mismatched disturbance is divided into two parts, which are compensated for and attenuated, respectively. The Root‐Mean‐Square performance is applied to attenuate the disturbance influence. Different from the traditional performance, there is no requirement for the zero initial condition. This condition implies that the selection of the fault estimation observer's initial value should be the same as the initial value of the fault, which is difficult to achieve since the fault is unknown. Therefore, the proposed method is more practical. Finally, the effectiveness of the method is proved by the simulation results of a numerical example and the electrical system dynamics for the DC motor.