In the first phase of the DFG Priority Program on Cyber-Physical Networking (SPP 1914) several projects have been conducted that investigate approaches for joint communication and control. A highly relevant application area that has been targeted by the SPP initiative but not studied in any of the projects so far is smart grid control. Electrical grids are experiencing a dramatic change and will experience an even faster change in the upcoming decades, caused by a transition from a low number of big, inert power plants to a large number of small and dynamic power generators. Virtually all other critical infrastructure relies on a stable power grid. It is hence of utmost importance to preserve this stability and achieve the expected quality of frequency control.

This is currently realized by a hierarchical approach with local primary control (independently of other power generators) and secondary control in a central control room. This approach, however, relies on the availability of large mechanical inertia (which is only provided in big thermal power plants) and does not scale arbitrarily when the number of power generators is increased. In this project we propose a flat, but distributed (networked) frequency control where every power generator is part of a distributed control problem. A critical challenge is then given by the effective measurement of the system level frequency with respect to the bus level frequency as available to every power generator. This can be approached by the recently developed concept of a Frequency Divider. We expect, however, that this can not be realized entirely distributedly without aid of the communication system due to large and uncertain delays.

In REDeFiNE we devise a joint communication and control solution where parts of the control problem will be solved inside the communication system and information that is typically only available to the communication system will be used to improve the control process. We plan to investigate the opportunities of in-network processing to offload frequency estimations to the network. In this realm, network devices will be made capable of aggregating local views of connected power generators into a frequency prediction.

Frequency predictions based upon the aggregate of local information can help increasing the scalability of the control process, but are subject to uncertainties. In particular, communication delays add uncertainty in the time domain. The joint communication and control approach addressed in this proposal, however, can benefit from knowledge that is typically only available to the communication system such as current buffer levels and link qualities. This information can be used to estimate delays and reduce uncertainty. Our research will be complemented by our partners in the U. S., who investigate orthogonal optimization techniques for distributed frequency and voltage control in the scope of aDaptioN. Eventually, we expect this approach to enable a stable frequency control for the future power grid.

Contact

For questions and inquiries regarding the project REDeFiNE, please contact:

Mirko Stoffers
Cyber-Physical Systems
E-Mail: stoffers[at]comsys.rwth-aachen.de

René Glebke
Cyber-Physical Systems
E-Mail: glebke[at]comsys.rwth-aachen.de

Funding

This project is funded by Deutsche Forschungsgemeinschaft (DFG) as part of the Priority Programme "Cyber-Physical Networking" (SPP 1914).