  Motivated by an increase of renewable energy sources we propose a distributed
optimal Load Frequency Control scheme achieving frequency regulation and
economic dispatch. Based on an energy function of the power network we derive
an incremental passivity property for a well known nonlinear structure
preserving network model, differentiating between generator and load buses.
Exploiting this property we design distributed controllers that adjust the
power generation. Notably, we explicitly include the turbine-governor dynamics
where first-order and the widely used second-order dynamics are analyzed in a
unifying way. Due to the non-passive nature of the second-order
turbine-governor dynamics, incorporating them is challenging and we develop a
suitable dissipation inequality for the interconnected generator and
turbine-governor. This allows us to include the generator side more
realistically in the stability analysis of optimal Load Frequency Control than
was previously possible.
