Event-triggered sampling with packet losses

Abstract: The communication rate between the sensor and the supervisor in computer controlled systems is often limited. If multiple sensors are using the same communication link the limitation can compromise the control of the system, especially when wireless technology is used. To lower the communication rate new sampling methods have been evaluated. Event-triggered sampling has shown to give good results when it comes to sampling for control. This thesis presents a redundancy solution when a first order water tank plant is controlled by the use event-triggered sampling and the communication link between the sensor and the control algorithm is exposed to packet losses. The redundancy solution is constructed to give good performance in the tradeoff between low sampling rate and high quality of control. First, a deterministic sampled PID controller is developed and implemented on the plant. The PID controller is used as a reference solution in a comparison. Then, an event-triggered sampling and control solution is developed and implemented. The reference signal is distributed to the sensor and the event-triggered policy uses fresh level crossings in the control error to trigger samples. The event-triggered control algorithm uses proportional control to give fast responses to changes in the reference signal. Measurement losses are simulated to act as packet losses between the sensor and the supervisor. The redundancy solution is implemented and performances of the different cases are compared. The event-triggered solution shows good results compared to the PID solution, especially when the reference signal changes rarely. The results shows that the effects of measurement losses are an increased communication cost and a decreased tracking performance. More interesting, the effect of the redundancy solution is a restored tracking performance compared to when no losses occur. The negative effect is an increased communication cost compare to when no redundancy solution is used.