  An imperative condition for the functioning of a power-grid network is that
its power generators remain synchronized. Disturbances can prompt
desynchronization, which is a process that has been involved in large power
outages. Here we derive a condition under which the desired synchronous state
of a power grid is stable, and use this condition to identify tunable
parameters of the generators that are determinants of spontaneous
synchronization. Our analysis gives rise to an approach to specify parameter
assignments that can enhance synchronization of any given network, which we
demonstrate for a selection of both test systems and real power grids. Because
our results concern spontaneous synchronization, they are relevant both for
reducing dependence on conventional control devices, thus offering an
additional layer of protection given that most power outages involve equipment
or operational errors, and for contributing to the development of "smart grids"
that can recover from failures in real time.
