Impact of uncertainty propagation on the design of state estimation for hybrid ac-dc grids

In order to ensure safe and reliable operation of the grids of the future, hybrid ac-dc grids are being considered as a promising solution. Traditionally state estimation (SE) of hybrid ac-dc grids has been performed with sequential SE algorithms. In this paper the authors show the inherent problems of the sequential SE algorithms, especially due to the incorrect propagation of the uncertainty of the boundary bus quantities. Instead, a two-step SE accounting for the converter losses is proposed, which updates the boundary results of the ac and dc grids respectively, to improve the accuracy. Tests of a simple hybrid ac-dc grid are presented to show the flaws in the sequential SE algorithms and the benefits of the proposed two-step method. Furthermore the accuracy improvements achievable through the inclusion of the converter losses in the SE algorithm are presented.