In a recent article by Zamora-Cárdenas et al. and appeared in Journal of Electric Power System Research, a hybrid estimator which considers SCADA and PMU measurements for power systems with embedded VSC-HVDC links was proposed.
Intermittent energy sources such as wind power generation with relevance to requirements of modern electric power system is causing higher power transfer through transmission windows and improvement to properly match the required nodal balance between generation and demand of electric power in maintaining networks security and reliability is taken into consideration. However, Flexible AC Transmissions Systems (FACTS) technology and high voltage direct current links (HVDC) technology have demonstrated their capabilities and flexibilities in fully controlling active and reactive power flows through transmission components (Xiao-Ping et al, 2006).
Phasor Measurement Units (PMUs) and Global Positioning System (GPS) of satellites provide accurate and synchronized positive sequence phasor of voltage and currents from respective waveforms and measurements which are synchronized with respect to a common synchronizing system (Phadke,1993). These advantages gave birth to Energy Management System (EMS) whose primary function is the State Estimation (SE) process which is used to estimate all state variable values that determine the current operation state.
It’s well established (Gomez-Esposito et al, 2011) that integration of synchronized measurements provided by PMUs has improved the state estimation performance capability of SCADA-based SE. Based on PMUs advantage, formulation and code of SE must consider these measurements together with those provided by SCADA system to properly estimate nodal voltage profile of electric network along operating status of FACTS and VSC-HVDC. Research has been done on SE considering FACTS controllers and PMU measurements as practical implementation equations into WLS-based state estimation algorithm. Hence a SE approach of power systems considering PMU measurements and VSC-HVDC links is researched by Zamora-Cárdenas et al.
The computational implementation of the proposed hybrid state estimator has been carried out through a digital code which has been developed in C++ language under an object-oriented programing philosophy. In order to show the SE performance of the proposed hybrid state estimator considering VSC-HVDC transmission links, study case and simulation results was based on a real-life network such as the Mexican interconnected system. From the results obtained, it was clear that larger number of measurements results to higher CPU time since more measurements caused a larger Jacobian Matrix. Relative errors in terms of PMUs showed the estimated phase angles and voltage magnitudes of six VSC-HVDC, it was noted that relative errors of VSCs phase angles decrease when HVDC-PMU measurements are included.
It was also noted that the VSC magnitude vanish as the corresponding HVDC terminal are equipped with PMUs and number of PMU measurement increases. This shows improvement due to the fact that PMUs provide to the WLS-based state estimation algorithm.
In order to show the impact of PMUs on detection and identification of gross errors associated with critical measurements in HVDC controllers, two estimations were performed; when PMU are and are not installed at both terminals of coupling transformers. SE process converged in sixth iterations with optimality function value of J(x) = 1.37907e_5 and threshold of X2 = 184.473 (J<X2) when PMUs were not installed showing failures in detecting gross errors. When PMUs were installed at both terminals, SE algorithm converged in the eight iterations with J(x) = 116705>X2=277.602 which shows detection and identification of measurement associated with gross error respectively. After removing the erroneous measurements, SE converged in fifth iterations with J(x) =2.33287e_5<X2=276.492.
Zamora-Cárdenas et al research hereby developed a proposed hybrid SE which proved to not only increase local accuracy of HVDC but also accuracy of whole networks estimated variables.
Xiao-Ping, C. Rehtanz, B. Pal, Flexible AC Transmission Systems: Modelling and Control, Springer, Heidelberg, Germany, 2006.
A.G. Phadke, Synchronized phasor measurements in power systems, IEEE Com- put. Appl. Power 6 (April (2)) (1993) 10–15.
Gómez-Expósito, A. Abur, P. Rousseaux, A. de la Villa Jaén, C. Gómez-Quiles, On the use of PMUs in power system state estimation, in: 17th Power Systems Computation Conference, Stockholm, Sweden, August, 2011, pp. 1–13.
E.A. Zamora-Cárdenas, C.R. Fuerte-Esquivel, A. Pizano-Martinez, H.J. Estrada-García. Hybrid State Estimator Considering SCADA and Synchronized Phasor Measurements in VSC-HVDC Transmission Links. Electric Power Systems Research, 2016, Volume 133, pp 42-50.
E.A. Zamora-Cárdenas1, C.R. Fuerte-Esquivel2, A. Pizano-Martínez1, H.J. Estrada-García1 . Hybrid state estimator considering SCADA and synchronized phasor measurements in VSC-HVDC transmission links. Electric Power Systems Research, Volume 133, 2016, Pages 42–50.Show Affiliations
- Universidad de Guanajuato, Electrical Engineering Department, Salamanca, Guanajuato, Mexico
- Universidad Michoacana de San Nicolás de Hidalgo, Faculty of Electrical Engineering, Morelia, Michoacán, Mexico
Go To Electric Power Systems Research