Application-Oriented Reactive Power Management in German Distribution Systems Using Distributed Energy Resources

Nowadays, according to the technical connection guidelines in Germany (VDE-AR-N) for distributed energy resources (DERs), a relevant reactive power provision potential can be provided from the existing DERs in the German distribution grids. The German distribution system operators, therefore, could make use of the existing reactive power potential for providing different kinds of ancillary services. In this thesis, an application-oriented reactive power management concept is proposed and discussed. The proposed reactive power management concept is based on the quasi-linear relationship between reactive power provision from DERs and the induced reactive power changes at grid interfaces. The entire concept can be mainly described by two main parts, central determination of reactive power setpoints and local limitation of reactive power setpoints. Using this combination, the proposed concept allows the distribution system operators to enable a certain amount of reactive power flexibility at the grid interfaces without causing undesired local voltage problems in their own grids. In this thesis, the proposed reactive power management concept is firstly implemented for a real medium voltage grid Seebach in the South of Germany and investigated in a simulation environment. As result, the proposed concept enables a controllable reactive power exchange at the grid interface between high voltage and medium voltage levels. By applying it at the medium voltage level, together with different local voltage control strategies at the low voltage level, the proposed concept could enable a significant reduction of undesired reactive power exchange at the grid interface. Moreover, the proposed concept could enable a relevant reactive power provision potential at grid interfaces and can be adjusted and widely applied in other medium voltage grids. The proposed concept is also applied in a high voltage grid section Regensburg (in simulation environment) to fulfill the assumed reactive power requirements given by transmission system operator. The results show that the proposed reactive power management concept can also be applied at the high voltage level with minor adjustments. It could significantly improve the compliance with assumed reactive power requirements and reduce the required additional compensation devices and investments. Finally, the functionality as well as the feasibility of the proposed reactive power management concept is investigated in a laboratory environment by applying it on an industrial computer and by performing real-time controller-in-the-loop simulations. As results, the developed reactive power controller could show a reliable and stable control behavior with satisfactory control accuracy.