A generalized subspace least mean square method is presented for accurate and robust estimation of oscillation modes from exponentially damped power system signals. The method is based on the orthogonality of signal and noise eigenvectors of the signal autocorrelation matrix. Performance of the proposed method is evaluated using Monte Carlo simulation and compared with the Prony method. Test results show that the generalized subspace least mean square method is highly resilient to noise and significantly dominates the Prony method in tracking power system modes under noisy environments.

%B Electric Power Components and Systems %V 41 %P 1205 - 1212 %8 09/2013 %N 12 %! Electric Power Components and Systems %R 10.1080/15325008.2013.807896 %0 Journal Article %J IEEE Transactions on Power Systems %D 2013 %T Mode shape estimation algorithms under ambient conditions: A comparative review %A Luke Dosiek %A Ning Zhou %A John W. Pierre %A Zhenyu Huang %A Dan Trudnowski %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K power systems %X This paper provides a comparative review of five existing ambient electromechanical mode shape estimation algorithms, i.e., the Transfer Function (TF), Spectral, Frequency Domain Decomposition (FDD), Channel Matching, and Subspace Methods. It is also shown that the TF Method is a general approach to estimating mode shape and that the Spectral, FDD, and Channel Matching Methods are actually special cases of it. Additionally, some of the variations of the Subspace Method are reviewed and the Numerical algorithm for Subspace State Space System IDentification (N4SID) is implemented. The five algorithms are then compared using data simulated from a 17-machine model of the Western Electricity Coordinating Council (WECC) under ambient conditions with both low and high damping, as well as during the case where ambient data is disrupted by an oscillatory ringdown. The performance of the algorithms is compared using the statistics from Monte Carlo simulations and results from measured WECC data, and a discussion of the practical issues surrounding their implementation, including cases where power system probing is an option, is provided. The paper concludes with some recommendations as to the appropriate use of the various techniques. %B IEEE Transactions on Power Systems %V 28 %P 779 - 787 %8 05/2013 %N 2 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2012.2210570 %0 Journal Article %J IEEE Transactions on Power Systems %D 2013 %T A Numerical Solver Design for Extended-Term Time-Domain Simulation %A Chuan Fu %A James D. McCalley %A Tong, Jianzhong %K AA09-001 %K Automatic Switchable Network (ASN) %K RTGRM %K System Security Tools %X Numerical methods play an important role in improving efficiency for power system time-domain simulation. Motivated by the need to perform high-speed extended-term time-domain simulation (HSET-TDS) for online purposes, this paper presents design principles for numerical solvers of differential algebraic systems associated with power system time-domain simulation, focusing on DAE construction strategies, integration methods, nonlinear solvers, and linear solvers. We have implemented a design appropriate for HSET-TDS, and we have compared the proposed integration method, Hammer-Hollingsworth 4 (HH4), with Trapezoidal rule in terms of computational efficiency and accuracy, using the New England 39-bus system, an expanded 8775-bus system, and PJM 13 029-bus system. %B IEEE Transactions on Power Systems %V 28 %P 4926 - 4935 %8 11/2013 %N 4 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2011.2177674 %0 Conference Paper %B 2013 North American Power Symposium (NAPS) %D 2013 %T Online estimation of power system distribution factors — A sparse representation approach %A Chen, Yu Christine %A Alejandro D. Dominguez-Garcia %A Peter W. Sauer %K AARD %K Automatic Switchable Network (ASN) %K CERTS %K distribution factors %K phasor measurement units (PMUs) %K power system reliability %XThis paper proposes a method to compute linear sensitivity distribution factors (DFs) in near real-time without relying on a power flow model of the system. Instead, the proposed method relies on the solution of an underdetermined system of linear equations that arise from high-frequency synchronized measurements obtained from phasor measurement units. In particular, we exploit a sparse representation (i.e., one in which many elements are zero) of the desired DFs obtained via a linear transformation, and cast the estimation problem as an IO-norm minimization. As we illustrate through examples, the proposed approach is able to provide accurate DF estimates with fewer sets of synchronized measurements than earlier approaches that rely on the solution of an overdetermined system of equations via the least-squares errors method.

%B 2013 North American Power Symposium (NAPS) %I IEEE %C Manhattan, KS, USA %P 1 - 5 %8 09/2013 %R 10.1109/NAPS.2013.6666886 %0 Journal Article %J Electric Power Systems Research %D 2013 %T Proactive task scheduling and stealing in master-slave based load balancing for parallel contingency analysis %A Siddhartha Kumar Khaitan %A James D. McCalley %A Somani, Arun %K AA09-001 %K Automatic Switchable Network (ASN) %K RTGRM %K System Security Tools %X With increasing emphasis on analyzing N − k contingencies, use of parallel resources has become imperative. Parallelization imposes the requirement of load-balancing for achieving high resource usage efficiency. Conventional static allocation based scheduling techniques fail to achieve load balancing. To address this limitation, master-slave scheduling (MSS) has been used; however, in MSS, after task completion, slave processors wait for the next task to arrive leading to idle-wait. In the case of contention at master, the idle-wait could become significant and degrade the performance of the MSS algorithm. We present a technique to combine the advantage of proactive task scheduling and stealing with the simplicity of MSS. We refer to it as PTMSS. In PTMSS, master proactively queues an extra task at the slave processor, such that on completion of a task, the next task is immediately started. Further, when master runs out of the tasks, it steals a queued task from one slave and allocates to another slave which has completed its tasks. Simulation experiments have been conducted on a large power system with 13,029 buses and thousands of contingencies have been analyzed. The results show that PTMSS performs better than conventional MSS and also offers significant computational gains over serial execution. %B Electric Power Systems Research %V 103 %P 9 - 15 %8 10/2013 %! Electric Power Systems Research %R 10.1016/j.epsr.2013.04.005 %0 Journal Article %J IEEE Transactions on Power Systems %D 2012 %T The Characteristic Ellipsoid Methodology and its Application in Power Systems %A Jian Ma %A Yuri V. Makarov %A Ruisheng Diao %A Pavel V. Etingov %A Jeffery E. Dagle %A De Tuglie, Enrico %K AA07-002 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K Power system dynamics %K situational awareness %X The characteristic ellipsoid (CELL) method to monitor dynamic behaviors of a power system is proposed. Multi-dimensional minimum-volume-enclosing characteristic ellipsoids are built using synchronized phasor measurements. System dynamic behaviors are identified by tracking the change rate of the CELL's characteristic indices. Decision tree techniques are used to link the CELL's characteristic indices and the system's dynamic behaviors and to determine types, locations and related information about the dynamic behaviors. The knowledge base of representative transient events is created by offline simulations based on the full Western Electric Coordinating Council (WECC) model. Two case studies demonstrate that the CELL method combined with the decision trees can detect transient events and their features with good accuracy. %B IEEE Transactions on Power Systems %V 27 %P 2206 - 2214 %8 11/2012 %N 4 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2012.2195232 %0 Journal Article %J IEEE Transactions on Power Systems %D 2012 %T A Stepwise Regression Method for Estimating Dominant Electromechanical Modes %A Ning Zhou %A John W. Pierre %A Dan Trudnowski %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K Power system stability %K RTGRM %X Prony analysis has been applied to estimate inter-area oscillation modes using phasor measurement unit (PMU) measurements. To suppress noise and signal offset effects, a high-order Prony model usually is used to over-fit the data. As such, some trivial modes are intentionally added to improve the estimation accuracy of the dominant modes. Therefore, to reduce the rate of false alarms, it is important to distinguish between the dominant modes that reflect the dynamic features of a power system and the trivial modes that are artificially introduced to improve the estimation accuracy. In this paper, a stepwise-regression method is applied to automatically identify the dominant modes from Prony analysis. A Monte Carlo method is applied to evaluate the performance of the proposed method using data obtained from simulations. Field-measured PMU data are used to verify the applicability of the proposed method. A comparison of results obtained using the proposed approach with results from a traditional energy-sorting method shows the improved performance of the proposed method. %B IEEE Transactions on Power Systems %V 27 %P 1051 - 1059 %8 05/2012 %N 2 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2011.2172004 %0 Conference Paper %B 2011 North American Power Symposium (NAPS 2011) %D 2011 %T Evaluation of mode estimation accuracy for small-signal stability analysis %A Jim Follum %A Ning Zhou %A John W. Pierre %K AA09-002 %K AARD %K Automatic Switchable Network (ASN) %K load modeling %K power system monitoring %X This paper proposes a method for determining electromechanical mode estimate accuracy by relating mode estimate error to residual values. Mode frequency and damping ratio were estimated using Prony analysis and residuals were calculated for a 17-machine model with varying levels of load noise. Mode estimate error and residuals were found to increase proportionally to each other as noise values were increased, revealing a distinctly linear relationship. The use of these results to develop appropriate confidence in models is discussed. With the relationship established, a method of predicting mode estimate error values based on residuals in the western North American power system (wNAPS) was developed. The potential of this method to evaluate the confidence level of mode estimates is examined. %B 2011 North American Power Symposium (NAPS 2011) %I IEEE %C Boston, MA, USA %P 1 - 7 %8 08/2011 %@ 978-1-4577-0417-8 %R 10.1109/NAPS.2011.6024893 %0 Conference Paper %B IEEE Power and Energy Society (PES) General Meeting %D 2011 %T The influence of topology changes on inter-area oscillation modes and mode shapes %A Yousu Chen %A Jason C. Fuller %A Ruisheng Diao %A Ning Zhou %A Zhenyu Huang %A Francis K. Tuffner %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K damping %K power grid operations %K Power system stability %K WECC %XThe topology of a power grid network is a piece of critical information for power grid operations. Different power grid topologies can change grid characteristics, inter-area oscillation modes, mode shapes, and even the robustness of the power system. This paper presents some preliminary study results, based on an approved WECC operating case and a modified low damping WECC system, to show the impact of topology changes resulting from N-1 contingencies on power system modes and mode shapes. The results show that topology changes can have very different impact on modal properties in a power system: some result in an unstable situation, while others can improve small signal stability. For the former, the studies show about a 4.5% damping reduction, so a 5% damping margin would be required to ensure the system can sustain the contingencies. For the latter, those topology changes could be used as a control method to improve small signal stability. Mode shapes normally do not change when there is an N-1 topology change. These observations suggest that the inclusion of topological information is useful for improving the accuracy and effectiveness of power system control schemes.

%B IEEE Power and Energy Society (PES) General Meeting %I IEEE %C Detroit, MI, USA %P 1 - 7 %8 07/2011 %@ 978-1-4577-1000-1 %R 10.1109/PES.2011.6039904 %0 Conference Paper %B IEEE Power and Energy Society (PES) General Meeting %D 2011 %T A modified stepwise linear regression method for estimating modal sensitivity %A Ning Zhou %A Zhenyu Huang %A Francis K. Tuffner %A Dan Trudnowski %A William A. Mittelstadt %K AA09-002 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K power system reliability %XSmall signal stability problems are one of the major threats to grid stability and reliability. Low damping of inter area modes is usually considered to be a result of heavy power transfer over long distances. This paper proposes a modified stepwise regression method to estimate the modal sensitivity with respect to power flow on the transmission lines based on measurement. This sensitivity is used to identify dominant transmission lines, whose power flow has significant influence on the inter-area modal damping. It is shown through simulation study that the proposed method can effectively estimate the modal sensitivity with respect to line power flow. This, in turn, provides insight on how to improve damping through adjusting tie line flow.

%B IEEE Power and Energy Society (PES) General Meeting %I IEEE %C Detroit, MI, USA %P 1 - 7 %8 07/2011 %@ 978-1-4577-1000-1 %R 10.1109/PES.2011.6039795 %0 Journal Article %J IEEE Transactions on Power Systems %D 2011 %T Transition to a Two-Level Linear State Estimator—Part II: Algorithm %A Tao Yang %A Sun, Hongbin %A Anjan Bose %K AA05-002 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K smart grid %X The availability of synchro-phasor data has raised the possibility of a linear state estimator if the inputs are only complex currents and voltages and if there are enough such measurements to meet observability and redundancy requirements. Moreover, the new digital substations can perform some of the computation at the substation itself resulting in a more accurate two-level state estimator. The main contribution in this paper is that this two-level processing removes the bad data and topology errors, which are major problems today, at the substation level. In Part I of the paper, we describe the layered architecture of databases, communications, and the application programs that are required to support this two-level linear state estimator. In Part II, we describe the mathematical algorithms that are different from those in the existing literature. As the availability of phasor measurements at substations will increase gradually, this paper describes how the state estimator can be enhanced to handle both the traditional state estimator and the proposed linear state estimator simultaneously. This provides a way to immediately utilize the benefits in those parts of the system where such phasor measurements become available and provides a pathway to transition to the "smart" grid of the future. %B IEEE Transactions on Power Systems %V 26 %P 54 - 62 %8 02/2011 %N 1 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2010.2050077 %0 Conference Paper %B 2011 44th Hawaii International Conference on System Sciences (HICSS) %D 2011 %T Use of Modal Sensitivity to Operating Conditions for Damping Control in Power Systems %A Zhenyu Huang %A Ning Zhou %A Francis K. Tuffner %A Dan Trudnowski %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K damping %K oscillations %K power system control %K Power system dynamics %K Power system stability %XSmall signal stability is an inherent characteristic of dynamic systems such as power systems. Pole positioning through power system stabilizers (PSS) is often used for improving damping in power systems. A well-designed PSS can be very effective in damping oscillations, especially local oscillations. However, designing PSSs for inter-area oscillations has been a very challenging task due to time-varying operating conditions affecting the oscillations. This paper explores the sensitivity relationship between oscillations and operating conditions, and employs the relationship to derive recommendations for operator's actions to adjust operating conditions for improving damping. Low damping is usually considered to be a result of heavy power transfer in long distance, while specific locations also have significant impact on damping of oscillations. Therefore, it is important to consider locations in deriving recommendations. This paper proposes the concept of relative modal sensitivity and presents its application in deriving recommendations for operator's action in damping control.

%B 2011 44th Hawaii International Conference on System Sciences (HICSS) %I IEEE %C Kauai, HI %P 1 - 9 %8 01/2011 %@ 978-1-4244-9618-1 %R 10.1109/HICSS.2011.469 %0 Conference Paper %B IEEE Power and Energy Society (PES) General Meeting %D 2010 %T Automatic implementation of Prony analysis for electromechanical mode identification from phasor measurements %A Ning Zhou %A Zhenyu Huang %A Francis K. Tuffner %A John W. Pierre %A Shuangshuang Jin %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K grid reliability %K phasor measurement units (PMUs) %K power system monitoring %XSmall signal stability problems are one of the major threats to grid stability and reliability. Prony analysis has been successfully applied on ringdown data to monitor electromechanical modes of a power system using phasor measurement unit (PMU) data. To facilitate an on-line application of mode estimation, this paper develops a recursive algorithm for implementing Prony analysis and propose an oscillation detection method to detect ringdown data in real time. By automatically detecting ringdown data, the proposed method helps to guarantee that Prony analysis is properly and timely applied on the ringdown data. Thus, the mode estimation results can be performed reliably and timely. The proposed method is tested using Monte Carlo simulations based on a 17-machine model and is shown to be able to properly identify the oscillation data for on-line application of Prony analysis.

%B IEEE Power and Energy Society (PES) General Meeting %I IEEE %C Minneapolis, MN %P 1 - 8 %8 07/2010 %@ 978-1-4244-6549-1 %R 10.1109/PES.2010.5590169 %0 Journal Article %J IEEE Transactions on Power Systems %D 2010 %T A Class of New Preconditioners for Linear Solvers Used in Power System Time-Domain Simulation %A Siddhartha Kumar Khaitan %A James D. McCalley %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K CERTS %K Power system modeling %K power system reliability %K RTGRM %X In this paper, a new class of preconditioners for iterative methods is proposed for the solution of linear equations that arise in the time-domain simulation of the power system. The system of linear equations results from an attempt to solve the differential algebraic equations (DAE) encountered in the power system dynamic simulation. The preconditioners are based on the multifrontal direct methods. The proposed method is compared to the incomplete LU factorization (ILU) based preconditioned iterative methods and other conventional direct linear sparse solvers. The comparison shows the proposed method achieves great computational efficiency relative to these other methods. %B IEEE Transactions on Power Systems %V 25 %P 1835 - 1844 %8 11/2010 %N 4 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2010.2045011 %0 Journal Article %J IEEE Transactions on Power Systems %D 2010 %T Fast Newton-FGMRES Solver for Large-Scale Power Flow Study %A Zhang, Yi-Shan %A Hsiao-Dong Chiang %K AARD %K Automatic Switchable Network (ASN) %K load flow %K RM11-008 %X A fast Newton-FGMRES method for power flow calculations is proposed in this paper. Three accelerating schemes to speed up the Newton-FGMRES method are proposed. Numerical studies show that the proposed fast Newton-FGMRES method consistently outperforms the traditional Newton-GMRES method and Newton-LU method on two practical power systems-one with 12 000 buses, another with 21 000 buses. For the 21 000-bus system, the fast Newton-FGMRES method can be 45.7% faster than the traditional Newton-LU method. %B IEEE Transactions on Power Systems %V 25 %P 769 - 776 %8 05/2010 %N 2 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2009.2036018 %0 Conference Paper %B IEEE PES General Meeting %D 2010 %T Improving small signal stability through operating point adjustment %A Zhenyu Huang %A Ning Zhou %A Francis K. Tuffner %A Yousu Chen %A Dan Trudnowski %A William A. Mittelstadt %A John F. Hauer %A Jeffery E. Dagle %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K Power system stability %X ModeMeter techniques for real-time small-signal stability monitoring continue to mature, and more and more phasor measurements are available in power systems. It has come to the stage to bring modal information into real-time power system operation. This paper proposes to establish a procedure for Modal Analysis for Grid Operations (MANGO). Complementary to PSS and other traditional modulation-based control, MANGO aims to provide suggestions such as redispatching generation for operators to mitigate low-frequency oscillations. Load would normally not be reduced except as a last resort. Different from modulation-based control, the MANGO procedure proactively maintains adequate damping at all times, rather than reacting to disturbances when they occur. The effect of operating points on small-signal stability is presented in this paper. Implementation with existing operating procedures is discussed. Several approaches for modal sensitivity estimation are investigated to associate modal damping and operating parameters. The effectiveness of the MANGO procedure is confirmed through simulation studies of several test systems. %B IEEE PES General Meeting %I IEEE %C Minneapolis, MN %P 1 - 8 %8 07/2010 %@ 978-1-4244-6549-1 %R 10.1109/PES.2010.5589519 %0 Conference Paper %B IEEE Power and Energy Society (PES) Transmission and Distribution Conference %D 2010 %T Initial studies on actionable control for improving small signal stability in interconnected power systems %A Francis K. Tuffner %A Zhenyu Huang %A Ning Zhou %A Ross T. Guttromson %A Jayantilal, Avnaesh %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K Power system modeling %XPower consumption and demand continues to grow around the world. As the electric power grid continues to be put under more stress, the conditions of instability are more likely to occur. One cause of such instabilities is intearea oscillations, such as the oscillation that resulted in the August 10, 1996 blackout of the WECC. This paper explores different potential operations of different devices on the power system to improve the damping of these interarea oscillations using two different simulation models.

%B IEEE Power and Energy Society (PES) Transmission and Distribution Conference %I IEEE %C New Orleans, LA, USA %P 1 - 6 %8 04/2010 %@ 978-1-4244-6546-0 %R 10.1109/TDC.2010.5484340 %0 Conference Paper %B 2010 43rd Hawaii International Conference on System Sciences (HICSS) %D 2010 %T Merging PMU, Operational, and Non-Operational Data for Interpreting Alarms, Locating Faults and Preventing Cascades %A Mladen Kezunovic %A Ce Zheng %A Pang, Chengzong %K AA05-003 %K AARD %K Automatic Switchable Network (ASN) %K energy management systems %K phasor measurement units (PMUs) %XWith the development of synchronized sampling technique and other advanced measurement approaches, the merging of various substation data to be used in new applications in the EMS solutions has not yet been explored adequately. This paper deals with the integration of time correlated information from Phasor Measurement Units, SCADA and non-operational data captured by other intelligent electronic devices such as protective relays and digital fault recorders, as well as their applications in alarm processing, fault location and cascading event analysis. A set of new control center visualization tools shows that the merging of PMU, operational and non-operational data could improve the effectiveness of alarm processing, accuracy of fault location and ability to detect cascades.

%B 2010 43rd Hawaii International Conference on System Sciences (HICSS) %I IEEE %C Honolulu, Hawaii, USA %P 1 - 9 %8 01/2010 %@ 978-1-4244-5509-6 %R 10.1109/HICSS.2010.271 %0 Journal Article %J Energy Systems %D 2010 %T Numerical methods for on-line power system load flow analysis %A Siddhartha Kumar Khaitan %A James D. McCalley %A Raju, Mandhapati %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %X Newton-Raphson method is the most widely accepted load flow solution algorithm. However LU factorization remains a computationally challenging task to meet the real-time needs of the power system. This paper proposes the application of very fast multifrontal direct linear solvers for solving the linear system sub-problem of power system real-time load flow analysis by utilizing the state-of-the-art algorithms for ordering and preprocessing. Additionally the unsymmetric multifrontal method for LU factorization and highly optimized Intel® Math Kernel Library BLAS has been used. Two state-of-the-art multifrontal algorithms for unsymmetric matrices namely UMFPACK V5.2.0 and sequential MUMPS 4.8.3 (“Multifrontal Massively Parallel Solver”) are customized for the AC power system Newton-Raphson based load flow analysis. The multifrontal solvers are compared against the state-of-the-art sparse Gaussian Elimination based HSL sparse solver MA48. This study evaluates the performance of above multifrontal solvers in terms of number of factors, computational time, number of floating-point operations and memory, in the context of load flow solution on nine systems including very large real power systems. The results of the performance evaluation are reported. The proposed method achieves significant reduction in computational time. %B Energy Systems %V 1 %P 273 - 289 %8 8/2010 %N 3 %! Energy Syst %R 10.1007/s12667-010-0013-6 %0 Journal Article %J IEEE Transactions on Power Systems %D 2010 %T Probing Signal Design for Power System Identification %A John W. Pierre %A Ning Zhou %A Francis K. Tuffner %A John F. Hauer %A Dan Trudnowski %A William A. Mittelstadt %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K WECC %X This paper investigates the design of effective input signals for low-level probing of power systems. In 2005, 2006, and 2008 the Western Electricity Coordinating Council (WECC) conducted four large-scale system-wide tests of the western interconnected power system where probing signals were injected by modulating the control signal at the Celilo end of the Pacific DC intertie. A major objective of these tests is the accurate estimation of the inter-area electromechanical modes. A key aspect of any such test is the design of an effective probing signal that leads to measured outputs rich in information about the modes. This paper specifically studies low-level probing signal design for power-system identification. The paper describes the design methodology and the advantages of this new probing signal which was successfully applied during these tests. This probing input is a multi-sine signal with its frequency content focused in the range of the inter-area modes. The period of the signal is over 2 min providing high-frequency resolution. Up to 15 cycles of the signal are injected resulting in a processing gain of 15. The resulting system response is studied in the time and frequency domains. Because of the new probing signal characteristics, these results show significant improvement in the output SNR compared to previous tests. %B IEEE Transactions on Power Systems %V 25 %P 835 - 843 %8 05/2010 %N 2 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2009.2033801 %0 Conference Paper %B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %D 2009 %T Decision tree assisted controlled islanding for preventing cascading events %A Ruisheng Diao %A Vijay Vittal %A Sun, Kai %A Kolluri, Sharma %A Mandal, S. %A Galvan, F. %K AA05-001 %K AARD %K Automatic Switchable Network (ASN) %K distributed generation %K phasor measurement units (PMUs) %XAt stressed operating conditions, critical contingencies can initiate loss of synchronism and trigger cascading events. Controlled islanding is the last line of defense to stabilize the whole system. This paper presents a decision tree assisted scheme to determine the timing of controlled islanding in real time by using phasor measurements. In addition, a slow coherency based approach is used to determine where to island. This scheme is tested on the operational model of the Entergy system and a severe N-2 outage case is used to demonstrate the phenomenon of cascading events due to protective relay actions. The results show that training one decision tree only for a specified critical contingency that can potentially cause cascading events can yields high prediction accuracy. Being aware of loss of synchronism in real time, operators can implement controlled islanding at carefully designed transmission interfaces and rapidly stabilize each island. Thus a significant amount of load is still served compared to uncontrolled system islanding.

%B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %I IEEE %C Seattle, WA, USA %P 1 - 8 %8 03/2009 %@ 978-1-4244-3810-5 %R 10.1109/PSCE.2009.4839985 %0 Conference Paper %B 2009 IEEE Power & Energy Society General Meeting %D 2009 %T Electromechanical mode shape estimation based on transfer function identification using PMU measurements %A Ning Zhou %A Zhenyu Huang %A Luke Dosiek %A Dan Trudnowski %A John W. Pierre %K AA07-001 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K Power system modeling %X Power system mode shapes are a key indication of how dynamic components participate in low-frequency oscillations. Traditionally, mode shapes are calculated from a linearized dynamic model. For large-scale power systems, obtaining accurate dynamic models is very difficult. Therefore, measurement-based mode shape estimation methods have certain advantages, especially for the application of real-time small signal stability monitoring. In this paper, a measurement-based mode shape identification method is proposed. The general relationship between transfer function (TF) and mode shape is derived. As an example, a least square (LS) method is implemented to estimate mode shape using an autoregressive exogenous (ARX) model. The performance of the proposed method is evaluated by Monte-Carlo studies using simulation data from a 17-machine model. The results indicate the validity of the proposed method in estimating mode shapes with reasonably good accuracy. %B 2009 IEEE Power & Energy Society General Meeting %I IEEE %C Calgary, Canada %P 1 - 7 %8 07/2009 %@ 978-1-4244-4241-6 %R 10.1109/PES.2009.5275924 %0 Journal Article %J IEEE Transactions on Power Delivery %D 2009 %T GridStat: A Flexible QoS-Managed Data Dissemination Framework for the Power Grid %A Gjermundrod, H. %A Gjermundrod, H. %A David E. Bakken %A Hauser, C.H. %A Anjan Bose %K AA05-002 %K AARD %K Automatic Switchable Network (ASN) %K PSERC %X With the increase in the monitoring of operational data at very high rates in high voltage substations and the ability to time synchronize these data with global positioning systems, there is a growing need for transmitting this data for monitoring, operation, protection, and control needs. The sets of data that need to be transferred and the speed at which they need to be transferred depend on the application-for example, slow for postevent analysis, near real time for monitoring and as close to real time as possible for control or protection. In this paper, we describe GridStat, a novel middleware framework we have developed to provide flexible, robust, and secure data communications for the power grid's operations. Test results demonstrate that such a flexible framework can also guarantee latency that is suitable for fast wide-area protection and control. %B IEEE Transactions on Power Delivery %V 24 %P 136 - 143 %8 01/2009 %N 1 %! IEEE Trans. Power Delivery %R 10.1109/TPWRD.2008.917693 %0 Journal Article %J IEEE Transactions on Power Systems %D 2009 %T Power System Risk Assessment and Control in a Multiobjective Framework %A Fei Xiao %A James D. McCalley %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K CERTS %K power system security %K RTGRM %K System Security Tools %X Traditional online security assessment determines whether the system is secure or not, but how secure or insecure is not explicitly indicated. This paper develops probabilistic indices, risk, to assess real-time power system security level. Risk captures not only event likelihood, but also consequence. System security level associated with low voltage and overload can be optimally controlled, using the NSGA multiobjective optimization method. A security diagram is used to visualize operating conditions in a way that enables both risk-based and traditional deterministic views. An index for cascading overloads is used to evaluate the Pareto optimal solutions. This paper shows that the multiobjective approach results in less risky and less costly operating conditions, and it provides a practical algorithm for implementation. The IEEE 24-bus RTS-1996 system is analyzed to show that risk-based system security control results in lower risk, lower cost, and less exposure to cascading outages. %B IEEE Transactions on Power Systems %V 24 %P 78 - 85 %8 02/2009 %N 1 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2008.2004823 %0 Conference Paper %B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %D 2009 %T The problem of initiating controlled islanding of a large interconnected power system solved as a Pareto optimization %A Vijay Vittal %A Gerald T. Heydt %K AA05-001 %K AARD %K Automatic Switchable Network (ASN) %K controlled islanding %K electricity markets %K Power system dynamics %K power system economics %XControlled islanding of a large electric power system is proposed under rare circumstances as a measure of last resort to avoid a catastrophic blackout. Controlled islanding appears to be more desirable than uncontrolled islanding. A separate power system operating objective is the retention of synchronous operation of the entire system to ensure the viability of power markets. The problem of when to initiate controlled islanding, accounting for power marketing objectives is formulated as a multiobjective optimization. Pareto optimization is applied in the form of the calculation of a Pareto surface. This formulation may allow power system operators to manage the multiobjectives of mitigating the possibility of a blackout versus the full enabling of power markets. This is a conceptual paper in which the analytical basis and the main points of the solution of when to initiate controlled islanding are outlined. The objective function recommended for the capture of transient stability is the transient stability load margin.

%B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %I IEEE %C Seattle, WA, USA %P 1 - 7 %8 03/2009 %@ 978-1-4244-3810-5 %R 10.1109/PSCE.2009.4839928 %0 Conference Paper %B IEEE Power & Energy Society (PES) General Meeting %D 2009 %T Risk-based optimal power flow and system operation state %A Li, Yuan %A James D. McCalley %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K load flow %K optimal power flow (OPF) %K power system economics %K power system reliability %XIn this paper, the risk-based optimal power flow is proposed, which minimizes the economic cost considering the system reliability, and a refined system operation state is provided to clarify this approach. In order to obtain better economic benefit than traditional security-constrained optimal power flow, the corrective optimal power flow is used in this work. The reliability is represented by the risk index, which captures the expected impact to the system. This problem is solved by Benders decomposition. The specific designed Benders subproblem will assure that no collapse or cascading overload occurs for the corrective optimal power flow problem. The approach auto-steers the dispatch between different risk level according to the probability and consequence of the upcoming contingency events. Case studies with a six-bus system are presented.

%B IEEE Power & Energy Society (PES) General Meeting %I IEEE %C Calgary, Canada %P 1 - 6 %8 07/2009 %@ 978-1-4244-4241-6 %R 10.1109/PES.2009.5275724 %0 Conference Paper %B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %D 2009 %T Two-level PMU-based linear state estimator %A Tao Yang %A Sun, Hongbin %A Anjan Bose %K AA05-002 %K AARD %K Automatic Switchable Network (ASN) %K phasor measurement units (PMUs) %K power system control %XThe State Estimator function in a control center today is a suite of three programs solved sequentially: topology processing, state estimation, and bad data detection-identification. The state estimation equations are nonlinear because the inputs are mostly real and reactive power measurements. A linear state estimator is possible if the inputs are only complex currents and voltages and if there are enough such measurements to meet observability and redundancy requirements. The main contribution in this paper is the suggestion that the topology processing function and the bad data detection-identification be done at each substation rather than at the control center. It is shown how this two-level processing is faster and more accurate leaving the control center level state estimator solution free of the bad data errors that are major problems today.

%B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %I IEEE %C Seattle, WA, USA %P 1 - 6 %8 03/2009 %@ 978-1-4244-3810-5 %R 10.1109/PSCE.2009.4840218 %0 Journal Article %J IEEE Transactions on Power Systems %D 2008 %T Design of Wide-Area Damping Controllers for Interarea Oscillations %A Zhang, Yang %A Anjan Bose %K AA05-002 %K AARD %K Automatic Switchable Network (ASN) %K oscillations %K Power system stability %X This paper develops a systematic procedure of designing a centralized damping control system for power grid interarea oscillations putting emphasis on the signal selection and control system structure assignment. Geometric measures of controllability/observability are used to select the most effective stabilizing signals and control locations. Line power flows and currents are found to be the most effective input signals. The synthesis of the controller is defined as a problem of mixed H 2/H infin output-feedback control with regional pole placement and is resolved by the linear matrix inequality (LMI) approach. A tuning process and nonlinear simulations are then used to modify the controller parameters to ensure the performance and robustness of the controller designed with linear techniques. The design process is tested on the New England 39-bus ten-machine system. %B IEEE Transactions on Power Systems %V 23 %P 1136 - 1143 %8 08/2008 %N 3 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2008.926718 %0 Journal Article %J IEEE Transactions on Power Systems %D 2008 %T Multifrontal Solver for Online Power System Time-Domain Simulation %A Siddhartha Kumar Khaitan %A James D. McCalley %A Qiming Chen %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K dynamic simulations %K Power system dynamics %XThis paper proposes the application of unsymmetric multifrontal method to solve the differential algebraic equations (DAE) encountered in the power system dynamic simulation. The proposed method achieves great computational efficiency as compared to the conventional Gaussian elimination methods and other linear sparse solvers due to the inherent parallel hierarchy present in the multifrontal methods. Multifrontal methods transform or reorganize the task of factorizing a large sparse matrix into a sequence of partial factorization of smaller dense frontal matrices which utilize the efficient Basic linear algebra subprograms 3 (BLAS 3) for dense matrix kernels. The proposed method is compared with the full Gaussian elimination methods and other direct sparse solvers on test systems and the results are reported.

%B IEEE Transactions on Power Systems %V 23 %P 1727 - 1737 %8 11/2008 %N 4 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2008.2004828 %0 Journal Article %J IEEE Transactions on Power Systems %D 2007 %T Risk-Based Security and Economy Tradeoff Analysis for Real-Time Operation %A Fei Xiao %A James D. McCalley %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K optimal power flow (OPF) %K Power system modeling %K power system security %K risk analysis %X This letter describes a new perspective on balancing system security level with cost for real-time operation. Security level is quantified using risk, which provides that security may be optimized. A risk-based multiple-objective (RBMO) model, considering security and economy together, is compared with the traditional security-constrained OPF (SCOPF) model. A six-bus test system is used to show the merits of RBMO. %B IEEE Transactions on Power Systems %V 22 %P 2287 - 2288 %8 11/2007 %N 4 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2007.907591