Monitoring of power system dynamics using a hybrid state estimator

Abstract

Modern power systems are undergoing a transformation process where distributed energy re-sources together with complex load technologies are increasingly integrated. This, in addition to a sustained growth in electricity consumption and a lack of significant investment in trans-mission infrastructure, leads power systems to face with new stochastic operating behavior and dynamics and to operate under stressed conditions. Under such operating conditions, the occurrence of a potential disturbance may cause a partial or a total collapse. Therefore, in order to minimize the risk of collapses and their impact, new monitoring tools must be adopted, capable of providing the right conditions for dynamic wide-area monitoring. The thesis presents a hybrid state estimator, that is a monitoring tool that combines fast synchronized phasor measurements with traditional measurements into a single scheme. It has the ability to estimate at high speed power system dynamics associated to slow and fast transient phenomena considering a reduced amount of phasor measurement units (PMUs). The developed scheme consists of two phases depending on the power system operating regime. In phase one the system is in stationary regime and bus voltages (magnitude and angle) together with related variables like power flows, current through lines, etc. are estimated by a static estimator at a low speed, which is determined by the supervisory control and data acquisition (SCADA) system. When a physical disturbance happens and the system is in transient regime phase two comes into operation. This time, two estimators work in sequence at high speed. First, a static state estimator is used to estimate bus voltages as soon as the synchronized phasor measurement set arrives. Then, a dynamic estimator is in charge of estimating dynamic states of all generators and motors in the system, even if the unit is not observed by a PMU. Full observability is re-stored through a novel data-mining based methodology, which defines, first, a PMU topology that allows monitoring the post-contingency bus voltage dynamics of the entire power system and, second, generates a number of bus voltage pseudo-measurements to extend the observability to the whole system.