Control Synthesis for Large Collections of Systems with Mode-Counting Constraints

Given a large homogeneous collection of switched systems, we consider a novel class of safety constraints, called mode-counting constraints, that impose restrictions on the number of systems that are in a particular mode. We propose an approach for synthesizing correct-by-construction switching protocols to enforce such constraints over time. Our approach starts by constructing an approximately bisimilar abstraction of the individual system model. Then, we show that the aggregate behavior of the collection can be represented by a linear system, whose system matrices are induced by the transition graph of the abstraction. Finally, the control synthesis problem with mode-counting constraints is reduced to a cycle assignment problem on the transition graph. One salient feature of the proposed approach is its scalability; the computational complexity is independent of the number of systems involved. We illustrate this approach on the problem of coordinating a large collection of thermostatically controlled loads while ensuring a bound on the number of loads that are extracting power from the electricity grid at any given time.