Verifying Average Dwell Time by Solving Optimization Problems

In the switched system model, discrete mechanisms of a hybrid system are abstracted away in terms of an exogenous switching signal which brings about the mode switches. The Average Dwell time (ADT) property defines restricted classes of switching signals which provide sufficient conditions for proving stability of switched systems. In this paper, we use a specialization of the Hybrid I/O Automaton model to capture both the discrete and the continuous mechanisms of hybrid systems. Based on this model, we develop methods for automatically verifying ADT properties and present simulation relations for establishing equivalence of hybrid systems with respect to ADT. Given a candidate ADT for a hybrid system, we formulate an optimization problem; a solution of this problem either establishes the ADT property or gives an execution fragment of the system that violates it. For two special classes of hybrid systems, we show that the corresponding optimization problems can be solved using standard mathematical programming techniques. We formally define equivalence of two hybrid systems with respect to ADT and present a simulation relation-based method for proving this equivalence. The proposed methods are applied to verify ADT properties of a linear hysteresis switch and a nondeterministic thermostat.