Verifying Band Convergence for Sampled Control Systems

We present a method to verify transient and settling time properties, called band convergence properties, of digitally controlled continuous systems, wherein we consider a linear dynamical system model for a plant and a PID controller. We consider the discrete-time sampled behavior of the closed loop system, and verify band convergence for the discrete-time behavior. The basic idea is to look for a box-shaped invariant for the system which is adequate to ensure that the system stays within the given band. We first give a technique to handle a general discrete-time system, but with determinate matrix entries. We then give a technique to handle discrete-time systems with matrices that lie in a range which over-approximate the matrix exponentials (which arise when we consider the discrete-time version of a continuous system), using the notion of an abstract discrete-time system. We have implemented the verification approach, and evaluate its efficacy on some popular Simulink models.

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