On Vinnicombe metrics and the stability robustness of linear time-varying systems

We present two novel approaches for obtaining stability robustness information about linear time-invariant systems with norm-bounded time-varying output multiplicative perturbations using Vinnicombe metrics. First, a time-varying Vinnicombe metric approximation between a nominal linear time-invariant system and the perturbed linear time-varying system is developed, and we show that a calculable tight upper bound may be placed on the approximation for a subclass of small, periodic output multiplicative errors. Second, we show that a worst-case time-invariant Vinnicombe metric may be used to obtain stability robustness information about the perturbed time-varying system.