Output feedback stabilizability and passivity in nonstationary and nonlinear systems

What is it about?

Positive realness has been shown to be very important for the stability of various methodologies of control with uncertainty in linear-time-invariant systems. Many publications have defined the conditions that allow linear time-invariant systems to become strictly positive real with constant or dynamic output feedback. As beyond the usual uncertainty, real-world systems are not necessarily invariant, this paper expands the applicability of previous results to nonstationary and nonlinear systems. The paper first reviews a few pole-zero dynamics definitions in nonstationary systems and relates them to stability and passivity of the systems. The paper then finds the sufficient conditions that allow nonstationary systems to become stable and strictly passive via static or dynamic output feedback. Applications in robotics and adaptive control are also presented.

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