Decentralized three-phase distribution system static state estimation based on phasor measurement units

Abstract

This paper presents a novel approach for static state estimation in electrical distribution systems, in which the state variables to be estimated are branch currents in rectangular coordinates. Branch current and voltage phasors are measured from a reduced number of PMUs located along a non fully observable electrical distribution system with radial topology. For the non-monitored buses, load pseudo-measurements are considered as a set of inequality constraints varying between upper and lower limits, which are adjusted during the safety barrier interior point optimization solution process (SBIPM). In order to track daily load variations, the initial load limits for the next time interval are obtained from the actual estimated loads at the non-monitored buses, considering the percentage of power variation at the exit of each lateral feeder. At each iteration of the SBIPM solution process, if any load is set to its corresponding limit, then a new limit margin is set accordingly, meaning that at the end of the solution process all the non-monitored loads are within specified bounds. The distribution network is also subdivided into subsystems considering a PMU allocation procedure in which each lateral feeder is estimated individually, yielding a naturally decentralized state estimator. In this decentralization context, priority loads, such as hospitals, police stations, telecom centers and places with high load density concentration can be considered as monitored subareas, exploring the radial topology of the distribution system. Tests are conducted on IEEE 33 bus test feeder and compared with an existing method in the literature to show the effectiveness of the proposed algorithm. Another simulation was conducted on a long lateral feeder of 57 bus in order to show the possibility of using the proposed technique for large scale distribution systems.