Power System Observability with Minimal Phasor Measurement Placement

Abstract

This paper deals with the placement of a minimal set of phasor measurement units (PMU’s) so as to make the system measurement model observable, and thereby linear. A PMU placed at a bus measures the voltage as well as all the current phasors at that bus, requiring the extension of the topological observability theory. This concerns the extension of the concept of spanning tree to that of spanning measurement subgraph with an actual or a pseudo-measurement assigned to each of its branches. The minimal PMU set is found through a dual search algorithm which uses both a modified bisecting search and a simulated annealing-based method. The former fixes the number of PMU's while the latter looks for a placement set that leads to an observable network for a fixed number of PMU's. In order to accelerate the procedure, an initial PMU placement is provided by a graph-theoretic procedure which builds a spanning measurement subgraph according to a depth-first search. From computer simulation results performed on various test systems it appears that only one fourth to one third of the system buses need to be provided with PMU's in order to make the system observable. © 1993 IEEE