Managing quality-of-control performance under overload conditions

A common method for dealing with overload conditions in periodic task systems is to reduce the load by enlarging activation periods. When a periodic task implements a digital controller, however the variation applied on the task period also affects the control law, which needs to be recomputed for the new activation rate. If computing a new control law requires too much time to be performed at runtime, a set of controllers has to be designed off line for different rates and the system has to switch to the proper controller in the presence of an overload condition. In this paper we present a method for reducing the number of controllers to be designed off line, while still guaranteeing a given control performance. The proposed approach has been integrated with the elastic scheduling theory to promptly react to overload conditions. The effectiveness of the proposed approach has been verified through extensive simulation experiments performed on an inverted pendulum.