  A key quality of any kind of system is its ability to deliver its respective
service correctly. Often the unavailability of commercial systems may lead to
lost revenue, which are minor compared to what may be at stake when critical
infrastructures fail. A failure to deliver critical services, such as clean
water or electricity may have dire consequences that endanger human lives and
may even halt or break other infrastructures. The services provided by critical
infrastructures need to be supplied continuously even when faced with
re-configurations, outside disturbances and systemic changes. A system is
called resilient if it fulfils this property. From the many critical
infrastructures that exist, power systems may be the most important ones,
because they are supplying the required electricity for other critical
infrastructures. At the same time, a power system itself may be exposed to
several disturbances from internal sources, e.g., fluctuations in the energy
demand, and external sources, e.g., heavy storms. Especially, fast dynamic
effects caused by these disturbances may lead to deviations of grid frequency,
short-circuits, or, in severe cases, a total power system failure. As future
scenarios will include more distributed renewable sources and less centralized
generation from fossil fuels, ICT-based communication and coordination will
play an increasing role. This paper examines the notion of resilience, how it
has been traditionally ensured for the power system, and novel approaches to
maintain the frequency, protect people and devices against short circuits and
recover from a blackout. A special focus is on communication and the role that
distributed renewable generation plays for these processes.
