Nikolaos M. Manousakis

Taxonomy of PMU Placement Methodologies

Utilization of phasor measurement units (PMUs) in the monitoring, protection and control of power systems has become increasingly important in recent years. The aim of the optimal PMU placement (OPP) problem is to provide the minimal PMU installations to ensure full observability of the power system. Several methods, based on mathematical and heuristic algorithms, have been suggested for the OPP problem. This paper presents a thorough description of the state of the art of the optimization methods applied to the OPP problem, analyzing and classifying current and future research trends in this field.

A Weighted Least Squares Algorithm for Optimal PMU Placement

This letter presents a new method for optimal placement of phasor measurement units (PMU) for complete power system observability. The optimal PMU placement (OPP) problem is formulated as a quadratic minimization problem with continuous decision variables subject to nonlinear observability constraints. The optimal solution is obtained by an unconstrained nonlinear weighted least squares (WLS) approach. Simulations are conducted on different IEEE systems (14-bus, 30-bus, 57-bus, and 118-bus) to prove the validity of the proposed algorithm.

Optimal placement of phasor measurement units: A literature review

The increasing availability of phasor measurement units (PMUs) at substations enables the synchronized measurements to various applications, such as the monitoring of system state under normal operations or the protection and control of power systems during abnormal operation. The objective of the optimal PMU placement (OPP) problem is to determine a minimal set of PMUs such that the whole system is observable. To solve the OPP problem, mathematical programming, heuristic, and meta-heuristic optimization techniques, have been proposed. This paper provides a comprehensive literature review on the OPP problem and the solution methodologies. Due to the vast number of publications in this field, the most representative papers are reviewed.

Power System Real-Time Monitoring by Using PMU-Based Robust State Estimation Method

Accurate real-time states provided by the state estimator are critical for power system reliable operation and control. This paper proposes a novel phasor measurement unit (PMU)-based robust state estimation method (PRSEM) to real-time monitor a power system under different operation conditions. To be specific, an adaptive weight assignment function to dynamically adjust the measurement weight based on the distance of big unwanted disturbances from the PMU measurements is proposed to increase algorithm robustness. Furthermore, a statistical test-based interpolation matrix H updating judgment strategy is proposed. The processed and resynced PMU information are used as priori information and incorporated to the modified weighted least square estimation to address the measurements imperfect synchronization between supervisory control and data acquisition and PMU measurements. Finally, the innovation analysis-based bad data (BD) detection method, which can handle the smearing effect and critical measurement errors, is presented. We evaluate PRSEM by using IEEE benchmark test systems and a realistic utility system. The numerical results indicate that, in short computation time, PRSEM can effectively track the system real-time states with good robustness and can address several kinds of BD.

A state estimation algorithm for monitoring topology changes in distribution systems

This paper proposes a state estimation algorithm for the monitoring of topological changes in distribution networks, using real measurements at substations, pseudo measurements at load and distributed generation buses, and zero injections at transition buses. This is accomplished by a generalized state estimation formulation, based on a weighted least squares approach with equality constraints, which involves both real and pseudo analog measurements and operational constraints for the switching devices. Estimates of state variables and switching device statuses are simultaneously provided. The normalized residual test is used to effectively identify gross errors in analog and topological data. The network splitting problem, caused by switching operations, is also investigated by introducing appropriate pseudo measurements. An advantage over previous methods is that the proposed approach eliminates the need of repeated state estimation runs for alternative hypothesis evaluation. A 17-bus distribution network is employed to demonstrate its effectiveness.

A state estimator including conventional and synchronized phasor measurements

This paper presents an effective weighted least square formulation for the solution of the state estimation problem, considering conventional as well as synchronized phasor measurements. The proposed algorithm is based on a reference-free formulation, using both rectangular and polar coordinates for branch current phasor measurements, and alleviates any numerical problems encountered during initialization stage of the state estimation algorithm. Analytical equations are provided for the conventional and the phasor measurements and their corresponding partial derivatives with respect to state variables. The proposed algorithm is tested with a seven bus system and is compared with the traditional state estimator. Simulation results show that the proposed algorithm improves the precision greatly and gets better behavior as compared with the traditional state estimator.

Optimal PMU Placement for Numerical Observability Considering Fixed Channel Capacity—A Semidefinite Programming Approach

This letter presents a 0-1 semidefinite programming (SDP) approach to solve the problem of optimal placement of phasor measurement units (PMUs), considering the existence of conventional measurements and zero injections as well as the impact of PMU channel limits. The proposed formulation can prevent the wasteful utilization of different PMUs observing incident branch current phasors at a given bus more than once. The method is tested on the IEEE 57-bus test system.

Optimal Placement of Phasor Measurement Units with Linear and Non-linear Models

Abstract—This article presents a non-linear programming-based model for the optimal placement of phasor measurement units. The optimal phasor measurement units placement is formulated to minimize the number of phasor measurement units required for full system observability and to maximize the measurement redundancy at all buses in a power system. A sequential quadratic programming algorithm is used for the solution of the proposed model. The existence of power flow and injection measurements, the limited phasor measurement units channel capacity, the lack of communication facilities in substations, and the single phasor measurement units loss are also incorporated into the initial proposed formulation. The non-linear programming model is applied to IEEE 14- and 118-bus test systems in MATLAB. The accuracy and the effectiveness of the proposed method is verified by comparing the simulation results to those obtained by a binary integer programming model also implemented in MATLAB. The comparative study shows that the proposed non-linear programming model yields the same number of phasor measurement units as the binary integer programming model. A remarkable advantage of the non-linear programming against binary integer linear programming is its capability to give more than one optimal solution, each one having the same minimum number of phasor measurement units (same minimum objective value), but at different locations.

A two-stage state estimator for power systems with PMU and SCADA measurements

Recent investments in the synchrophasor technology have drastically increased the availability of phasor measurement units (PMUs) at selected substations, improving the monitoring, protection, and control of modern power systems. This paper presents a two-stage state estimation model based on measurements provided by PMUs and SCADA (supervisory control and data acquisition) system. At the first stage, a linear state estimator is formulated, using only the synchronized phasor measurements provided by PMUs. At the second stage, the estimated voltage phasors from the first stage and the SCADA measurements are simultaneously processed by a conventional non-linear state estimator to determine the whole system state. The performance of the proposed algorithm is evaluated in terms of convergence and accuracy. Simulations are conducted on the IEEE 57 and the Polish 2383-bus systems in order to validate the efficiency of the proposed algorithm.

Observability analysis and restoration for state estimation using SCADA and PMU data

This paper presents a hybrid topological/numerical method for power system observability analysis, using conventional measurements, provided by SCADA, as well as synchronized phasor measurements, provided by phasor measurement units (PMUs). A PMU placed at a bus can measure the voltage phasor at that bus, as well as the current phasors in some or all the lines connected to that bus. Branch power flow and current phasor measurements are used to build topologically flow islands that, in turn, are used to construct a reduced network. A gain matrix associated with this reduced network is built, considering boundary injections at flow islands and all bus voltage phasors. Observability checking is carried out analyzing the pivots in the triangular factors of this gain matrix and observable islands are identified in a noniterative manner, by performing back substitutions. Additional measurements for observability restoration are provided by a direct method, using the triangular factors of a reduced Gram matrix associated with existing and candidate injections as well as PMUs at boundary buses of the observable islands. The IEEE 14 and 30 bus systems illustrate the steps of the proposed method.