Switched Linear Ensemble Systems and Structural Controllability

Abstract: This paper introduces and solves a structural controllability problem for ensembles of switched linear systems. All individual subsystems in the ensemble are sparse, governed by the same sparsity pattern, and undergo switching at the same sequence of time instants. The controllability of an ensemble system describes the ability to use a common control input to simultaneously steer every individual system. A sparsity pattern is called structurally controllable for pair ((k,q)) if it admits a controllable ensemble of (q) individual systems with at most (k) switches. We derive a necessary and sufficient condition for a sparsity pattern to be structurally controllable for a given ((k,q)), and characterize when a sparsity pattern admits a finite (k) that guarantees structural controllability for ((k,q)) for arbitrary $q$. Compared with the linear time-invariant ensemble case, this second condition is strictly weaker. We further show that these conditions have natural connections with maximum flow, and hence can be checked by polynomial algorithms. Specifically, the time complexity of deciding structural controllability is (O(n^3)) and the complexity of computing the smallest number of switches needed is (O(n^3 \log n)), with (n) the dimension of each individual subsystem.