Observability analysis for power systems including conventional and phasor measurements

This paper presents a numerical method for observability analysis of a measurement system including phasor measurement units (PMUs) as well as conventional measurements. Traditional power flow measurements and branch current phasor measurements are used to build topologically flow islands that, in turn, are used to construct a reduced network. Boundary injections at flow islands and bus voltage phasors are considered to form a reduced size Jacobian matrix. Observability checking is carried out analyzing the pivots encountered during the triangular factorization of a Gram matrix associated with this reduced order Jacobian. The additional measurements, that restore the global observability of an unobservable system, are provided by a direct method, using the triangular factors of a Gram matrix associated with a reduced Jacobian including existing and candidate traditional injection measurements as well as PMUs, at boundary buses of the flow islands. The IEEE 14-bus system demonstrates the features of the proposed method.