State feedback controller for distributed systems with non-deterministic time delays

Physical distribution of modules of a closed loop control system, i.e., sensor, controller and actuator over a communication network, is the state of the art in the modern motion control industry. The gains are to reduce system wiring, ease of fault diagnosis, maintenance etc. Inserting a communication network to connect the sensor to controller and controller to actuator, makes the analysis and controller design complicated. Because the ideal centralized assumptions such as synchronized sensor and/or controller signal availability, non-delayed sensing and actuation are no longer valid. The network induced delays in communicating through a shared medium like standard Ethernet are hardly ever constant. The time varying non-deterministic nature of the delays, depending on their magnitudes compared to the time constants, can destabilize or at least degrade a system whose non-networked closed loop version is highly stable and well performing. This paper addresses the network induced delay problem by using time-stamps of the data packets in real-time computation of a full-state feedback controller. Performance of the method is verified using a test rig comprising a Brushless DC motor, whose speed control loop is closed via a standard Ethernet network. Further, the experimental results of the suggested method are compared with the performance of standard controller designs for systems with time delays.