With the development of phasor measurement unit (PMU) and communication technology

PMUs have evolved into practical equipment for state estimators

dynamic monitoring

stability controls and other aspects in power systems. It is neither possible nor necessary to place PMU at each bus to make the system observable. On the basis of network topological observability theory

a numerical formulation method is proposed to maximally simplify the nonlinear constraints by using mixed measurement set. The optimal PMU placement (OPP) is then expressed as a combinatorial optimization problem for the purpose of minimal PUM placement. Tabu search (TS) is also used to work out the OPP problem. The most attractive properties of the algorithm is that mixed measurement set is considered

i.e.

conventional power flows and injections together with phasor measurements for voltage and line currents are included. The validity and flexibility of the proposed algorithm are tested with IEEE 14-bus and IEEE 118-bus power system and the results show that less amount of PMU is needed to make the system observable compared to general OPP algorithm.