Abstract:Abstract-This paper develops formulas for the condition number of the state estimation problem as a function of the different types and number of measurements. We present empirical results using the IEEE RTS-96 and IEEE 118 bus systems that validate the formulas.
“…Note that the zero identification problem plagues all algebraic procedures to check observability. However, this problem can be mitigated by selecting the right number and type of measurements, as suggested in [23,24].…”
Section: Mathematical Bases and Rationalementioning
“…Note that the zero identification problem plagues all algebraic procedures to check observability. However, this problem can be mitigated by selecting the right number and type of measurements, as suggested in [23,24].…”
Section: Mathematical Bases and Rationalementioning
“…Additionally, the inverse of the Jacobian matrix condition number as used in Stéphant, Charara, and Meizel (2007) is introduced as an observability indicator, which gives a measure of the sensitivity of the solution to the observation problem. The condition number of a matrix is defined as the ratio of the largest singular value to the smallest one (Ebrahimian & Baldick, 2001).…”
“…Similarly, the two-stage approach described in [12] also requires more computational effort than the proposed method because it involves the QR factorization of an matrix followed by backward substitutions in the first stage as well as the inversion of a matrix in the second stage. 2) Improved Numerical Stability: Numerical stability depends critically on the condition number of the gain matrix of the Gauss-Newton iterations [26], [27]. The condition number of a matrix is the ratio of its largest eigenvalue to its smallest eigenvalue.…”
This paper presents a state estimation method for power systems when not all state variables are observable with phasor measurement units (PMU), namely, incomplete PMU observability. Realizing that PMU measurements are generally more accurate than conventional ones, the proposed approach estimates PMU unobservable states and PMU observable states separately. The latter are estimated from PMU measurements using a linear estimator. Those estimates are then used along with conventional measurements in a reduced-order nonlinear estimator for the PMU unobservable states. The proposed decoupled approach features reduced computational complexity and greater numerical stability, when compared to existing combined approaches. We show analytically that the performance of the proposed method is comparable to that of existing approaches if PMU measurements are sufficiently accurate. In this paper, we also study the impact of time-skew errors in conventional measurements on the performance of hybrid state estimators using both conventional and PMU measurements. We propose a model that incorporates such errors into conventional measurements. We show that our proposed method is more robust than existing approaches in the presence of time-skew errors. Our analytical findings are verified by simulations on standard IEEE test systems.
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