A new unified approach for the state estimation and bad data analysis of electric power transmission systems with multi-terminal VSC-based HVDC networks

The aim of this paper is the proposal of a static state estimation approach suitable for electric power transmission systems containing fully controlled multi-terminal high voltage direct current networks. An integrated electric circuit model of the voltage source converter station, including its on-load tap-changer (OLTC) transformer, is used to determine the state variables associated with the AC-DC interface. These controllable variables are added to the state vector, together with the nodal voltages associated with the AC and DC networks, as well as the duty cycle of the DC-DC converters, for a unified SE solution in a single frame of reference. The SE problem is formulated based on Hachtel's augmented matrix method in order to directly consider the operational constraints associated with the AC-DC network. In addition, a new technique for performing multiple bad data analysis is proposed in which the original level of measurement redundancy is maintained unaltered during the estimation process. The applicability of the proposed SE approach and bad data analysis is demonstrated by estimating the operating state of two integrated AC-DC multi-terminal transmission networks. The numerical results show that the proposal retains good convergence properties in terms of the number of iterations required to achieve a reliable state estimation as well as robustness to deal with bad data.