Real Time PMU-Based Stability Monitoring (S-50)

Real Time PMU-Based Stability Monitoring
Final Project Report
Power Systems Engineering Research Center
Empowering Minds to Engineer
the Future Electric Energy System
Real Time PMU-Based Stability Monitoring
Final Project Report
Project Team
Chen-Ching Liu, Project Leader
Washington State University
Umesh Vaidya
Iowa State University
A. P. Sakis Meliopoulos
Georgia Institute of Technology
PSERC Publication 14-11
October 2014
For information about this project, contact
Chen-Ching Liu
School of Electrical Engineering and Computer Science
Washington State University
Pullman, WA, 99164-2752
Email: [email protected]
Phone: 509-335-1150
Power Systems Engineering Research Center
The Power Systems Engineering Research Center (PSERC) is a multi-university Center
conducting research on challenges facing the electric power industry and educating the
next generation of power engineers. More information about PSERC can be found at the
Center’s website: http://www.pserc.org.
For additional information, contact:
Power Systems Engineering Research Center
Arizona State University
527 Engineering Research Center
Tempe, Arizona 85287-5706
Phone: 480-965-1643
Fax: 480-965-0745
Notice Concerning Copyright Material
PSERC members are given permission to copy without fee all or part of this publication
for internal use if appropriate attribution is given to this document as the source material.
This report is available for downloading from the PSERC website.
 2014 Washington State University. All rights reserved.
Acknowledgements
This is the final report for the Power Systems Engineering Research Center (PSERC)
research project titled “Real Time PMU-based Stability Monitoring” (project S-50). We
would like to express our appreciation for the support provided by PSERC’s industry
members and the National Science Foundation under the Industry / University
Cooperative Research Center program.
We thank Bonneville Power Administration (BPA) for the test data, and the support in
part by National Science Foundation CAREER grant ECCS 1150405. The project team is
very grateful to the industry advisors of the project for their contributions:
Alan Engelmann, Exelon/Commonwealth Edison
Bill Timmons, Western Area Power Administration
Clifton Black, Southern Company
David Schooley, Exelon/Commonwealth Edison
Dmitry Kosterev, Bonneville Power Administration
Eugene Litinov, ISO New England
Evangelos Farantatos, Electrical Power Research Institute
George Stefopoulos, New York Power Authority
Guiseppe Stanciulescu, BC Hydro
Jay Giri, ALSTOM Grid
Jinan Huang, Hydro-Québec Reseach Institute
Liang Min. Lawrence Livermore National Lab
Manu Parashar, ALSTOM Grid
Patrick Panciatici, Raidió Teilifís Éireann
Sanjoy Sarawgi, American Electric Power
Steven Hedden, Exelon/Commonwealth Edison
Xiaochuan Luo, ISO New England
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Executive Summary
The purpose of this project is to develop PMU-based, real-time, wide area stability
monitoring algorithms for the power grids using different methods and approaches.
Phasor Measurement Units (PMUs) are increasingly available on power grids due to the
significant investment in recent years, e.g., North America SynchroPhasor Initiative
(NASPI) and the introduction of PMU functionality in relays and fault recorders. As a
result, a priority in industry is to extract critical information from the increasing amount
of PMU data for operation, planning, protection, and control.
This research proposes new algorithms for real time stability monitoring in a control
center environment. Two distinct but complementary methods are proposed for PMUbased stability monitoring: (a) waveform analysis to extract the “trending” information of
system dynamics embedded in Lyapunov exponents – Is the system approaching
instability?, and (b) a real time stability analysis based on energy functions for a faulted
system – Will the system remain stable following the fault? The combination of these
approaches provide a comprehensive and predictive stability monitoring system that help
to avoid cascading failures and enhance system security.
Part I: Real Time PMU-Based Stability Monitoring
A PMU-based online waveform stability monitoring technique is proposed based on the
Maximum Lyapunov Exponent (MLE). The main idea of the MLE technique is to
calculate MLE as an index over a finite time window in order to predict unstable trending
of the operating conditions. Significant progress has been made to improve the accuracy
of MLE technique. First, the dynamic model of the power system is greatly improved by
adopting a structure preserving model taking into account the dynamics of P and Q load
with respect to the frequency/voltage variations. The purpose is to extend the MLE
technique to voltage stability analysis as well as rotor angle stability. Based on this
model, the system can be represented by a set of differential equations, which is suitable
for MLE calculation. The power network topology is preserved. Parameters for the model
are identified from the results of time domain simulation. Secondly, a new method has
been proposed to determine the proper time window of MLE in an online environment.
This method increases the accuracy of prediction given by MLE. At the same time, the
computational burden does not increase significantly and, therefore, make the MLE
technique more reliable for online monitoring. The proposed methods are validated by
time-domain simulation of 122-bus mini-WECC system.
Part II: Date-Driven Model-Free Approach for Real-Time Stability Monitoring
A data-driven model-free approach is developed for short-term voltage and rotor angle
stability monitoring of power systems. The approach is developed with regard to its
application for real-time PMU-based stability monitoring of power systems. The theory
behind the proposed approach is adopted from ergodic theory of dynamical systems. In
particular, Lyapunov exponent is utilized as an indicator of stability to measure the
exponential rate of convergence and divergence of nearby system trajectories following a
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fault or disturbance. The positive (negative) value of Maximum Lyapunov Exponent
implies exponential divergence (convergence) of nearby system trajectories and hence
unstable (stable) system dynamics. An algorithm is provided for the computation of
Maximum Lyapunov Exponent for the time-series data. The proposed algorithm can be
implemented in real-time. The proposed Lyapunov exponent-based stability approach is
also used to determine the stability/instability contributions of the individual buses to the
overall system stability and for computation of the critical clearing time. Various
practical issues are addressed with regard to the implementation of the proposed method,
such as phasor measurement noise, communication delay, and the finite window size for
prediction. Simulation results for rotor angle and voltage stability monitoring are
provided for IEEE 162 bus system to demonstrate the application of the developed
method. Finally, preliminary results on the implementation of the algorithm on a Real
Time Digital Simulator (RTDS) test bed are provided.
Part III: Predictive Transient Stability Monitoring
The objective of this task is to develop a predictive transient stability monitoring scheme
that utilizes the information given by the dynamic state estimation. The developed
method monitors the transient swings of the system and characterizes in real time the
stability of the system. It is capable of predicting whether the generator will reach an outof-step condition. The developed method can be utilized as a predictive out of step
protection scheme capable of detecting potential generator loss of synchronism before the
condition has occurred. As such it is an improvement over present day out of step
protection schemes.
This novel, predictive, transient stability monitoring scheme with an application to
generator out-of-step protection is presented in this report. In particular, the real-time
dynamic model of the system (as computed with the distributed state estimator) is utilized
to evaluate the system’s energy function based on Lyapunov’s direct method and
monitors the energy of the generator continuously in real time, in order to characterize
the stability of the generator. The two major components of the scheme are a) the
calculation of the center of oscillations of the system and b) the derivation of an
equivalent, reduced sized model which is used for the calculation of the potential and
kinetic energy of the generator. The total energy of the generator is tracked in real time as
the sum of the potential energy plus the kinetic energy. The total energy is compared to
the boundaries of the potential energy to determine the stability of the generator. Finally
an application of this scheme is described, a novel predictive generator out-of-step
protection scheme.
The report describes implementation details of the predictive stability monitoring system.
To predict generator stability accurately, the up-to-date system topology is needed during
the process of creating the equivalent system in the stability monitoring scheme. A novel
dynamic state estimation based protection scheme, aka setting-less protection, is
presented which detects faults and provides the system topology evolution whenever a
protection function acts and alters the topology of the system by tripping breaker(s). The
integration and coordination of the setting-less protection and the purposed stability
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monitoring scheme is described in the report. Together, they provide a completed, realtime, predictive generator out-of-step protection. The developed scheme is compared
with the state-of-the art technology for generator out-of-step protection, which is based
on impedance relays that monitor the impedance trajectory at the terminals of the
generator. The major advantage of the proposed scheme is that it predicts the out-of-step
condition before its occurrence and therefore relays can act much faster than today’s state
of art technology.
Project Publications:
1. H. Guo, C. -C. Liu, and G. Wang, “Lyapunov Exponents over Variable Window
Sizes for Prediction of Rotor Angle Stability,” Accepted for North American Power
Symposium, 2014.
2. S. Dasgupta, M. Paramasivam, U. Vaidya, and A. Venkataramana, “Real-Time
Monitoring of Short Term Voltage Stability Using PMU Data,” IEEE Trans. Power
Systems, Vol 28, No 4, pp 3702-3711, 2013.
3. S. Dasgupta, M. Paramasivam, U. Vaidya, and A. Venkataramana, “PMU-Based
Model-Free Approach for Real-Time Rotor Angle Monitoring,” Accepted for
publications in IEEE Power Engineering Letters, 2014.
4. S. Dasgupta, M. Paramasivam, U. Vaidya, and A. Venkataramana, “Entropy-Based
Metric for Characterization of Delayed Voltage Recovery,” Accepted for publication
in IEEE Trans. Power Systems, 2014.
5. A. Reddy, K. Ekmen, V. Ajjarapu, and U. Vaidya, “PMU Based Real-Time Short
Term Voltage Stability Monitoring Analysis and Implementation on a Real-Time Test
Bed,” Accepted for North American Power Symposium, 2014.
6. S. Dasgupta and U.Vaidya, “Theoretical Foundation for Finite Time Stability
Monitoring in Power systems,” Submitted to American Control Conference, 2015.
7. E. Farantatos, R. Huang, G. Cokkinides, and A. P. Meliopoulos, “A Transient
Stability Monitoring Scheme Enabled by a Distributed Dynamic State Estimator,”
submitted to the IEEE Transactions – under review.
8. E. Farantatos, R. Huang, G. Cokkinides, and A. P. Meliopoulos, “A Predictive
Generator Out-of-Step Protection Scheme Enabled by a Distributed Dynamic State
Estimator,” submitted to the IEEE Transactions – under review.
Student Theses:
1. H. Guo, “Lyapunov Exponents over Variable Window Sizes for Prediction of Rotor
Angle Stability,” Master Thesis, Washington State University, 2013.
2. Z. Lin, “Lyapunov Exponent Analysis for Power System Dynamic Monitoring Based
on Structure Preserving Model,” Master Thesis, Washington State University,
Expected Dec. 2014.
3. E. Farantatos, “A Predictive Out-Of-Step Protection Scheme Based On PMU Enabled
Distributed Dynamic State Estimation”, PhD Thesis, Georgia Institute of Technology,
December 2012.
4. L. Sun, "Rotating Electric Machine Setting-less Protection", PhD Thesis, Georgia
Institute of Technology, in progress.
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