Fuzzy scheduled gain middleware for networked control systems

Communication networks are fast and reliable medium of data transfer. When communication network is added in closed loop control system, it provides benefit of re-tuning or changing the controller parameters remotely. Addition of communication network in closed loop control system also induces delays within the loop. This induced delay degrades the performance of the closed loop system. Sometimes delays in the loop may produce instability. Effective approach is required to compensate this delay effect. In this paper, fuzzy scheduled gain middleware is introduced to compensate for this delay effect. This gain middleware enables the use of existing non-networked controllers to be used in a networked environment. Consequently it saves time and cost for designing new controllers. The gain middleware is an external gain added with the existing controller. The fuzzy logic scheduler adjusts the middleware gain on the basis of network delay estimated by delay estimator. Speed control of a DC motor by a PI controller is used as an illustrative example. Simulation results are included, which demonstrates the effectiveness of the proposed approach.