Modeling and small-signal stability analysis of decentralized energy sources implementing Q(U) reactive power control

Decentralized energy sources implement reactive power control strategies to reduce deviations of voltage magnitudes from nominal values at low- and medium-voltage levels. This paper studies the dynamics of a single Q(U)-controlled power converter that is connected to a grid. After introducing a model for converters that operate as current sources, a small-signal stability analysis is performed considering the influence of the reactive power control parameterization as well as grid parameter variations. Thus, the effects of crucial parameters on system stability are discussed for stiff and weak power grids from a control engineering point of view. Finally, the analytical results are validated by means of exemplary computer simulations.