A method for allocation of system model in communication disturbance observer considering unstable network

Time delay problem used to be dealt mainly in process or plant engineering in the early phase of time delay systems research. In recent years, time delay problem in network-based control systems has been attracting much attention. This kind of network is usually unstable, and time delay is time varying and unpredictable. As a time delay compensation method, Smith predictor was a famous and useful approach. However, this method uses time delay model to compensate for time delay effect and so it is not a practical method for network-based control systems. Thus, communication disturbance observer (CDOB) has been proposed to compensate for time delay effect without using a time delay model. However, a large steady state error occurs, if the network is unstable. This paper modifies the structure of a time-delayed control system with CDOB considering an unstable network. To reduce nonlinear effects such as jitter or packet dropouts, the allocation of the system model in the CDOB has been modified. Then, the robustness of the modified CDOB structure against packet dropouts and jitter is confirmed by simulation. The validity of the modified structure is shown by experimental results.