  The problem of decentralized frequency control in power networks has received
an increasing attention in recent years due to its significance in modern power
systems and smart grids. Nevertheless, generation dynamics including
turbine-governor dynamics, in conjunction with nonlinearities associated with
generation and power flow, increase significantly the complexity in the
analysis, and are not adequately addressed in the literature. In this paper we
show how incremental secant gain conditions can be used in this context to
deduce decentralized stability conditions with reduced conservatism.
Furthermore, for linear generation dynamics, we establish Popov-like conditions
that are able to reduce the conservatism even further by incorporating
additional local information associated with the coupling strength among the
bus dynamics. Various examples are discussed throughout the paper to
demonstrate the significance of the results presented.
