Analysis of interactions between regulated distribution transformers (RDT) and local voltage control Q(V) by means of the harmonic balance method

The increase of decentralized power generation in low voltage grids imposes new challenges on the conventional operating strategies for electrical grids, as power transmission used to predominantly pass from high voltage levels to low voltage levels. Distributed generation in low voltage grids lead to unprecedented voltage limit violations, which can efficiently be solved by implementing new control systems e.g. regulated distribution transformers (RDT) or local voltage control (e.g. Q(V)). Both correspond to closed-loop control systems and thus, are prone to stability issues and possible interactions with other control elements. Furthermore, the nonlinear characteristics of RDTs complicate the systems' stability analysis. This paper introduces the harmonic balance method as an approach to characterize the nonlinear behavior of an RDT and assess the system stability as well as possible interactions with other linear controllers in the electrical grid.