This paper aims to develop a PMU-based state estimation algorithm that considers the presence of classic HVDC links operating under different control modes. Thus, hybrid AC/DC grid state estimation becomes feasible. In this algorithm we assume that DC link measurements can be sampled and reported at the same rate as PMU measurements, so that both AC and DC states can be estimated simultaneously in real-time. The estimation algorithm uses synchrophasors in polar coordinates, which allows angle bias detection and correction. In addition, some practical issues for the proposed state estimator are discussed, including observability and measurement redundancy, measurement noise and weightings, and angle bias correction. Finally, study cases using different power system models are carried out to show the state estimator's performances during both steady conditions and dynamic changes. Relatively small residuals during steady conditions validate accuracy; results during dynamic changes verify the estimator's reliability.
Li, W., & Vanfretti, L. (2015). A PMU-based state estimator considering classic HVDC links under different control modes. Sustainable Energy, Grids and Networks, 2, 69–82. https://doi.org/10.1016/j.segan.2015.04.004