Anamitra Pal

Methodology for Performing Synchrophasor Data Conditioning and Validation

A phasor measurement unit (PMU) only state estimator is intrinsically superior to its SCADA analogue with respect to speed, performance, and reliability. However, ensuring the quality of the data stream which enters the linear estimator is crucial before establishing it as the front end of an EMS or other network applications. One approach is to pre-process the phasor data before it arrives at the linear estimator. This paper presents an algorithm for synchrophasor data conditioning and repair that fits neatly as a prefix into the existing linear state estimation formulation. The methodology has been tested using field data obtained from PMUs installed in Dominion Virginia Powers (DVPs) EHV network. The results indicate that the proposed technique provides a computationally simple, elegant solution to the synchrophasor data quality problem.

A PMU Placement Scheme Ensuring Real-Time Monitoring of Critical Buses of the Network

This paper presents a phasor measurement unit (PMU) placement scheme that provides real-time monitoring of key buses of the network. High-voltage lines, substations relevant for transient and dynamic stability of the network, and buses with high connectivity are given the highest priority while placing the PMUs. Binary integer programming and “depth of unobservability” are used to find the relevant PMU placement set. The placement scheme has been tested on the IEEE 118-bus system, IEEE 300-bus system, a 283-bus model of the Central American Power Transmission System, and a complex 996-bus network describing the Northern and the Eastern power grids of India. The results indicate that the proposed technique will be useful to utilities that want to initially protect the most important buses of their system on their way to attaining complete observability.

Dynamic state prediction based on Auto-Regressive (AR) Model using PMU data

This paper presents a dynamic state prediction method based on an Auto-Regressive Model (AR model) using PMU data. In recent years, state prediction has played a key role in improving power system performance and reliability. When load is increased linearly at a constant power factor, it is proved in this paper that the bus voltages are quadratic and the AR model for predicting the next voltage is based on three prior estimates. This logic is then tested on the IEEE-118 bus system. The test results demonstrate that under morning load pick-up, economic dispatch, line opening and generator oscillations, the proposed method is correct and gives valid predictions. Furthermore, based on the error in quadratic fit, it is advocated that this method could be applied to detect abnormal conditions in the transmission systems. Theoretical analysis and results show that the proposed method based on AR model has great potential in predicting power system states.

Co-ordinated control of inter-area oscillations using SMA and LMI

Selective Modal Analysis (SMA) has been used in the design of WAMS based damping of inter-area oscillations. In conjunction with a Linear Matrix Inequality (LMI) formulation and a polytopic model a single control law can be found to guarantee pole placement for multiple contingencies. The previous attempts have used a model containing all the ε and ω modes, with SMA used to eliminate all other states. In practical applications the resulting system is still too large to use in a polytopic model. This paper presents an algorithm to further reduce the system size to the relevant modes of oscillations. A 16 machine, 68 bus system is used as the test case with PSSs, DC lines and SVCs acting as the control.

Multi-Polytope-Based Adaptive Robust Damping Control in Power Systems Using CART

An adaptive damping control scheme based on classification and regression tree (CART) using wide-area signals is proposed in this paper. Different polytopes are chosen using classification trees. Next, a family of robust polytopic controllers is designed off-line. Finally, using regression trees and PMU data, the desired polytopic controller is identified in real time. A 16-generator, 68-bus system is used as the test system. Remote signals obtained from PMUs are employed for control purposes. The simulation results demonstrate that the proposed adaptive control scheme is able to provide adequate damping for the oscillation modes of interest with respect to varying operating conditions without any prior knowledge of the post-disturbance state.

A PMU Placement Scheme Considering Realistic Costs and Modern Trends in Relaying

Synchrophasor deployment costs have evolved over time. The cost of upgrading a substation, which is much larger than the cost of an individual device, has emerged as the primary constituent of the total expenditure. Given these circumstances, the optimal phasor measurement unit placement formulation needs to consider not only the number of devices that must be placed at the substations, but also the number of substations that must be upgraded to support those devices. This paper presents an integer linear programming methodology for such a placement scheme while considering realistic costs and practical constraints. The IEEE 30 bus system is used to illustrate the proposed concept, while the IEEE 118, IEEE 300, and Polish 2383 bus systems are used to show the performance of the method under different test environments.

Classification trees for complex synchrophasor data

Abstract Classification and regression trees (CART) has been used for various applications in power systems. In most of these applications, phasor data obtained from phasor measurement units are used for building the decision tree. However, the splits in CART are based on a single attribute or a combination of variables chosen by CART itself rather than the user. But as phasor measurement unit data are complex numbers, both the attributes—real and imaginary—should be considered simultaneously for making critical decisions. For example, changing the reference bus in situations where the split is only on the real or imaginary part of a complex voltage (or current) measurement can cause the performance of the tree to degrade significantly. An algorithm is proposed in this article to allow splits on complex synchrophasor data. The methodology is implemented on two systems: a detailed model of the California Power System, where it is used for developing an adaptive protection scheme, and the IEEE 118-bus system, where it is used to classify dynamic events based on trajectories of voltage measurements obtained from phasor measurement units. MATLAB® (The MathWorks, Natick, Massachusetts, USA) implementation of classification and regression trees (classregtree.m) has been used for performing both analyses.

A robust control technique for damping inter-area oscillations

In order to reduce the detrimental effects of inter-area oscillations on system stability, it is possible to use Linear Matrix Inequalities (LMIs) to design a multi-objective state feedback control. The LMI optimization comes up with a control law that stabilizes numerous operating conditions simultaneously using a polytopic model of the system. However, the number of cases to be considered is limited by computational complexity and increased chances of infeasibility. In order to circumvent this problem, this paper presents a method for solving multiple polytopic problems having a common base case. The proposed algorithm determines which polytopic control is necessary for a particular contingency and classifies them as belonging to that polytopic domain. The technique was tested on an 8-machine, 13 bus system and provided satisfactory results.

Online Calibration of Voltage Transformers Using Synchrophasor Measurements

Uncalibrated instrument transformers present at the inputs of phasor measurement units (PMUs) can significantly degrade their outputs. This also causes problems in downstream applications that use PMU data. This paper presents a method for calibrating voltage transformers online using synchrophasor measurements. The proposed approach aims to find the optimal locations where good quality measurements must be added in order to bring the calibration error of all the measurements below a predefined threshold. The IEEE 118-bus system, the IEEE 300-bus system, and a 2383-bus Polish system have been used as the test systems for this analysis. The advantage of the proposed approach is its effectiveness and robustness.

A Voltage Phasor Based Fault-classification Method for Phasor Measurement Unit Only State Estimator Output

Abstract—This article presents a fault-classification method for transmission lines based on voltage phasors using classification and regression trees. The proposed method is intended to aid system operators in understanding the outputs of a phasor measurement unit only state estimator. Faults are classified into four categories when the estimator is positive sequence and into ten categories when the estimator is three phase. The fault data are generated in PowerWorld® (PowerWorld Corporation, Champaign, IL, USA) and DSA Tools® (Powertech Labs Inc., Surrey, British Columbia, Canada). The pre-fault state consists of a variety of operating conditions and loading angles of faulted lines. The fault condition comprises different fault types, fault locations, fault impedances, and fault incidence angles. Fault classification is done using MATLAB® (The MathWorks, Natick, Massachusetts, USA).The approach is successfully tested on the IEEE-118 bus system. The results demonstrate that the technique developed here is effective and robust, irrespective of the pre-fault and fault conditions.