Design and Evaluation of a Mixed Time-Triggered and Event-Triggered Scheme for Distributed Control System (Masterthesis)
15. 09. 2014, 15:00, room 3945
The conventional approach for implementation of embedded control systems employs primarily two schemes. 1) the time-triggered(TT) scheme and 2) event-triggered(ET) scheme. The time-triggered scheme offers better determinism, dependability and possibility of schedule optimization. However, time-triggered scheme lacks flexibility and consumes more resource. On the other hand, the event-triggered scheme has a high flexibility, a better real-time performance and usually consumes less resource. But it lacks determinism and dependability. Recently, there have been some efforts in combining the TT and ET schemes in embedded control systems for more efficient resource utilization, which involves switching between the two schemes. The aim of this study is to realize another possibility of more resource-efficient flexible design, in which the both of the schemes are integrated into a holistic approach and executed at the same time. The TT scheme is used for providing basic control performance and ET scheme is for the performance enhancement. The first step is concentrated on design and development of this mixed scheme in SIMULATION environment and implementation of it on FlexRay bus systems. The second step involves the comparison of mixed scheme and pure T-T scheme in control performance for step response of conventional control plants and how the parameter configuration of mixed scheme affects the control performance is as well an important part of the experiments. The results show that the mixed scheme plays a great role in reducing the maximum overshoot of step response of control system and makes the response process more stable and smooth. Due to this character the mixed control scheme has a better control performance than pure T-T scheme when the response process is oscillating (e.g. P controller). However for a well-controlled system, which has a stable, smooth and accurate control response (e.g. PID controller), the mixed scheme in most cases has no efforts in improving the control performance. And the control performance of mixed scheme is related with the parameter in event-triggering condition, the sampling period of event-triggering and the latency of event-triggered communication.