Many renewable energy sources, such as wind or solar power, are uncertain by nature and thus not completely controllable. A large proportion of renewable sources comes from small-scale distributed generation and is connected to the low and medium voltage level. This is where also most loads can be found. Thus it seems natural to attempt balancing consumption and generation locally.
The resulting local (micro) grids may be connected to the main distribution network, but can also be operated in "island mode" during faults in the main grid. This scenario implies a number of challenging control problems, which we have recently started to investigate in cooperation with Siemens AG. These include choosing a suitable control architecture, handling the transition between connected and island modes and guaranteeing stability and performance in the presence of uncertainty which is inherent in renewable energy generation.