Flexible Electrical Networks FEN Research Campus
Flexible control of power flow is key for the modern electrical grid to react to fluctuations in generation and load. However, a flexible energy transfer through today’s medium-voltage ac networks is not feasible due to their radial structure. To increase the flexibility of conventional ac systems, different network nodes may be connected via DC grids.
In this context, research activities on medium-voltage dc systems are performed in RWTH University, supported by the Federal Ministry of Research and Education as part of the “Flexible Electrical Networks FEN Research Campus”. The research work is carried out in a collaborative framework between several RWTH institutes and companies in four interconnected projects on the following topics:
- network planning and design of hybrid ac-dc and pure dc grids,
- development of components for MVDC systems,
- integration of control and automation concepts in MVDC networks
- design and realisation of a life-size MVDC research grid.
The major contribution of ACS occurs in the topics of control strategies and automation systems. Substantial studies have been made in these fields in the case of ac systems, but control and automation of hybrid grids with meshed ac and dc parts is still a challenge, as classical concepts are not sufficient. Additionally, ACS cooperates with other institutes in the research area of network planning, as well as the development of test platforms and a real MVDC grid.
Network planning and design
This FEN project encompasses classical reinforcement and new automation concepts in a comprehensive manner. In this framework, ACS contributes to the transient stability analysis of hybrid ac-dc and pure dc grids for verification of their dynamic operation. Moreover, ACS develops algorithms for fault location identification according to grid measurements. These protection schemes play a key role in the analysis of different post-fault topologies for the self–healing of the system after a fault.
The development of control concepts for hybrid ac-dc and pure dc grids is the core goal of this project. ACS combines various control strategies (centralised, decentralised, distributed) with control methods (state feedback, synergetic control law, back stepping, etc.) to formulate the corresponding control algorithms. Major challenge is the definition of global and local control quantities in dc grids, as well as the introduction of system uncertainties, e.g. topology uncertainties, uncertainties of measurements, intermittent power generation, etc. For the assessment of the developed control algorithms system performance indices, like power quality indices and stability margins, are newly defined for dc grids, due to lack of current operation standards.
ACS will design in this project advanced monitoring and state estimation systems for hybrid ac-dc and pure dc grids. These methods are crucial for the realization of control functions, such as voltage regulation, and protection algorithms, like fault location identification. As these methods are used in the frame of the automation system, control and protection functions are mapped to the fundamental elements of the automation architecture, jointly developed in all its aspects, from communication, to data models and protocols, to accommodate these functionalities.
ACS will validate the developed control strategies and automation system on Hardware-in-the-Loop (HiL) and Power-Hardware-in-the-Loop (PHiL) test platforms, prior field tests. These set-ups in fact yield the validation of the operative implementation, not just of the concepts. The PHiL platform will be used in the mature stages of the project, as a test bench for real power equipment like dc-dc converters and dc circuit breakers.
MVDC research grid
One major goal of the FEN project is the construction of a life-size MVDC grid, connected to the ac network of the RWTH-Aachen university campus. This hybrid system is going to act as research grid for validating the developed control and protection algorithms that are implemented through the novel automation system. In this lighthouse activity, ACS will model the ac grid and interface the model with the real dc network to achieve large scale PHiL simulation.
On July 5th, industrial and academic partners participated in the first medium voltage consortium Workshop to discuss the results of the work achieved and define future directions for cooperation in research and development activities both industry and university.
The Forschungscampus for Flexible Electrical Networks was visited by the reviewers from University Kassel (Prof. Braun) and TU Ilmenau (Prof. Westermann) as well as representatives from Siemens and Projektträger Jülich.
Grateful acknowledgement is made to BMBF (German Federal Ministry of Education and Research) for providing financial support under the grant agreement no. 03SF0490.