Inclusion of HVDC links in AC power-system state estimation

The inclusion of HVDC links into power-system state estimation is described. A quite general, 11-state HVDC link model is chosen, and 25 possible HVDC link measurements are identified, as well as seven pseudo measurements which describe convertor-terminal conditions. It is shown that the AC terminal injections, together with the pseudo measurements, constitute a minimal measurement set for HVDC link observabiity. Performance of the AC-DC state estimator is investigated on a multi-AC-DC test system having 31 states and 59 measurements. Convergence in 4-5 iterations to a tolerance less than 0.00001 p.u. is obtained, provided AC slack (reference) bus bars are retained. Geographic partitioning of HVDC links is considered. This permits separate state estimation for each AC system and associated HVDC convertor terminal. Last, fast decoupled state-estimation schemes are developed and tested; only the AC portion of the multi-ACHVDC system can be fast decoupled. Inclusion of HVDC links in fast decoupled AC state estimation causes no increase in the number of iterations and only a small increase in computation time