State Estimation and Voltage Phasor Measurements in Distribution Networks

The thesis faces the problem of the use of phasor measurement units (PMU) for the state estimation in distribution networks, and in particular the problem of a suitable phasor estimation in different buses of a distribution network in absence of proper time synchronization with the universal time reference. In particular, an approach recently proposed by Mingotti et al. to obtain an equivalent synchronization, starting from asynchronous measurement has been presented and tested. This method assumes the availability of a distributed measurement system where each remote unit is a power meter. The algorithm implemented in Matlab by Mingotti et al. has been studied and tested by a comparison with the load flow results provided by the Electromagnetic Transient Program (EMTP-RV). The algorithm adopts two different methods for voltage phasor estimation, the first calculate the phasors as a linear combination of measured voltages, the second makes use of the longitudinal equivalent impedances of the network branches. In order to tune the load flow calculation environment, different case studies have been analyzed, and in particular the European Medium Voltage distribution test network and the European Low voltage distribution test network proposed by CIGRE Task Force C6.04.02. During the analysis, for each bus, voltages, currents and phase displacements are calculated and compared with the benchmark results reported in the Cigré brochure. A four-buses network has been considered to test both methods of the above mentioned algorithm. The obtained results are very close to the one provided by EMTP. The accuracy of the algorithm appears to get worse in case of lightly loaded network, a behaviour that is justified by the small phase displacements that the voltages show in these condition. The studied equivalent synchronization procedure can be usefully implemented to achieve a widespread monitoring of a power network at affordable cost.