Hybrid state estimator considering SCADA and synchronized phasor measurements in VSC-HVDC transmission links

• A hybrid state estimation approach suitable for AC/DC power systemsis proposed.
• SCADA and PMU measurements are simultaneously processed in the proposed approach.
• A formulation of PMU measurements in VSC-HVDC links is derived from first principles.
• Network and VSC-HVDC variables are estimated under a unified framework of reference.
• Covariance errors of PMU's are recalculated with the uncertainty propagation theory.

This paper proposes a practical approach for implementing a hybrid state estimator by considering SCADA and PMU measurements in VSC-HVDC transmission links under a unified framework of reference. A proposed formulation for the PMU measurements associated with the VSC-HVDC state variables is derived from the first principles and is implemented into a weighted least square-based state estimation algorithm. In order to avoid numerical problems of convergence of the proposed state estimation approach, the set of current phasor measurements is represented in rectangular coordinates, such that their corresponding variances are also recalculated according to the uncertainty propagation theory. The state estimation process uses the measurement of one voltage phase angle as the global reference for the rest of voltage phase angles estimated at network buses and VSC-HVDC's voltage source converters. The proposed formulation improves the accuracy at which both network and VSC-HVDC state variables are simultaneously estimated based on the measurements provided by a SCADA system and PMUs. A Mexican interconnected 190-bus equivalent system is used as the test system in order to validate the effectiveness of the proposed hybrid state estimator.