On measuring closed-loop nonlinearity - a Vinnicombe metric approach

The focal point of this paper is to develop a measure of closed-loop nonlinearity. In this work, the Vinnicombe metric and the quasi-linear parameter varying representation of a nonlinear system are exploited for this purpose. It is expected that the proposed measure can serve as a decision making tool for control engineers when considering whether a linear or a nonlinear control strategy should be employed to close the loop.