HIERARCHICAL STATE ESTIMATION FOR WIDE AREA POWER SYSTEMS

This thesis presents the application of hierarchical state estimation techniques to consolidate the state output of a wide area power system network. In a wide area network a large number of interconnections exist between various utilities of the wide area. Power transactions between areas occur over large distances and hence for better security there is a need to monitor the state of the entire wide area systems. Hierarchical state estimation is preferred over integrated state estimation, due to the reduced computational time. Using existing state estimators of the member utilities of the wide area in the bottom level of hierarchical state estimation proves to be economical. The coordination level alone needs to be done using the state estimation output of the member areas for obtaining the overall state estimate. In this thesis a modified coordination technique derived from hierarchical state estimation is proposed to consolidate the state outputs of all the individual entities in the wide area. Issues due to heterogeneity of the estimators in each member utility of the wide area have been identified and addressed. A modification to the traditional hierarchical state estimation approach has been proposed which overcomes issues of delay and loss of state outputs from the estimators in the wide area. Use of synchronized phasor measurements in the hierarchical structure has been studied. The coordination algorithms have been tested on an IEEE 118 bus system by splitting the system into smaller areas. The results of the algorithms have been analyzed on the basis of accuracy and speed. The results of these algorithms have been compared to integrated state estimation of the wide area. The results show that the coordination algorithm is four times faster than the integrated state estimator without sacrificing the level of accuracy. To account for the issues regarding the delay of state output arrivals and the absence of state outputs from an area, the coordination algorithm of the hierarchical state estimation technique has been modified. As might be expected, the modified coordination algorithm decreases the accuracy of the overall state estimate. In contrast, the use of synchronized phasor measurements in all the levels of the hierarchical state estimator increases the confidence of the overall estimate apart from increasing the performance of the estimation process