Variable Selective Control Method for Networked Control Systems

A new method for the design of network-based control systems, together with mathematical tools for closed-loop stability assessment, is proposed. In order to preserve the closed-loop stability under random network time delays, the variable selective control (VSC) methodology is introduced, which combines the idea of variable sampling control with the packet-based control methodologies. In the proposed method, event-driven sensors are employed, which sample the plant output just after a new control input signal is received by the actuator. The advantages are as follows: 1) the latest actual sampling period becomes equal to the most recent time delay, which is known by direct measurement; 2) better estimation of the actual plant states can be performed in the predictive controller; 3) less frequent and shorter packets need to be transferred through the network; and 4) the stability analysis becomes simpler and does not depend on variable-size matrices. In order to deal with packet dropout issue, a simple, yet effective, algorithm is adopted in the controller, where packet losses are considered as variable time delays. In light of this formulation, the networked control system can be considered as a switched linear system and, therefore, previously existing theoretical results are adopted for stability analysis of the VSC method. Simulation studies on a well-known benchmark problem demonstrate the effectiveness of the proposed method.