With increasing renewable penetrations and advancements in power electronics associated with smart grid technologies, distributed control of the power grid is quickly becoming a necessity. Once communications are introduced into a control system, the impacts of latency and unreliable communications quickly become a priority. Vector Lyapunov techniques are well suited for the analysis of control systems with structured perturbations. These perturbations can be employed to model uncertainty in communications as well as parameter uncertainty. In this paper, we present results for small signal stability of a simplified two area power system model for several scenarios: bandwidth limited local communications and tie line uncertainty; local communications and bandwidth limited global communications combined with tie line uncertainty; and uncertainty in global communications. These results are intended to be a starting point for the analysis of the impact of communications uncertainty on the stability of power systems.

%B 2016 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM) %I IEEE %C Capri, Italy %P 1284 - 1291 %8 08/2016 %R 10.1109/SPEEDAM.2016.7526031 %0 Conference Paper %B 2016 IEEE Power and Energy Society General Meeting (PESGM) %D 2016 %T Supervisory system for a wide area damping controller using PDCI modulation and real-time PMU feedback %A Brian J. Pierre %A Ryan T. Elliott %A David A. Schoenwald %A Jason C. Neely %A Raymond H. Byrne %A Dan Trudnowski %A Colwell, James %K AA14-006 %XThis paper describes a control scheme to mitigate inter-area oscillations through active damping. The control system uses real-time phasor measurement unit (PMU) feedback to construct a commanded power signal to modulate the flow of real power over the Pacific DC Intertie (PDCI) located in the western North American Power System (wNAPS). A hardware prototype was constructed to implement the control scheme. To ensure safe and reliable performance, the project integrates a supervisory system to ensure the controller is operating as expected at all times. A suite of supervisory functions are implemented across three hardware platforms. If any controller mal-function is detected, the supervisory system promptly disables the controller through a bumpless transfer method. This paper presents a detailed description of the control scheme, simulation results, the bumpless transfer method, and a redundancy and diversity method in the selection of PMU signals for feedback. This paper also describes in detail the supervisory system implemented to ensure safe and reliable damping performance of the real-time wide area damping controller.

%B 2016 IEEE Power and Energy Society General Meeting (PESGM) %I IEEE %C Boston, MA, USA %P 1 - 5 %8 07/2016 %R 10.1109/PESGM.2016.7741594 %0 Conference Paper %B 2014 IEEE Power & Energy Society General Meeting %D 2014 %T Open-loop PDCI probing tests for the Western North American power system %A Dan Trudnowski %A Dmitry Kosterev %A Wold, Josh %K AA14-006 %K AARD %K CERTS %K synchrophasor-based control %XPoorly-damped electromechanical oscillations are of concern in the western North American power system. Recent development of reliable real-time wide-area measurement systems has enabled the potential for large-scale damping control approaches for stabilizing critical oscillation modes. The current approach being developed is feedback modulation of the Pacific DC Intertie (PDCI). This paper summarizes several years of open-loop actual-system PDCI probing tests. This includes a total of 56 tests conducted in 2009, 2011, and 2012. Test goals are to: 1) evaluate the controllability and robustness of the PDCI with WAMS feedback for damping; and 2) compare actual-system results to model-based transient stability and eigenanalysis studies.

%B 2014 IEEE Power & Energy Society General Meeting %I IEEE %C National Harbor, MD, USA %P 1 - 5 %8 07/2014 %R 10.1109/PESGM.2014.6939436 %0 Conference Paper %B 2014 IEEE Power & Energy Society General Meeting %D 2014 %T Optimal locations for energy storage damping systems in the Western North American interconnect %A Raymond H. Byrne %A Dan Trudnowski %A Jason C. Neely %A Ryan T. Elliott %A David A. Schoenwald %A Matthew K. Donnelly %K AA14-006 %K AARD %K CERTS %K damping %K HVDC %K oscillations %K phasor measurement units (PMUs) %K synchrophasor-based control %XElectromechanical oscillations often limit transmission capacity in the western North American Power System (termed the wNAPS). Recent research and development has focused on employing large-scale damping controls via wide-area feedback. Such an approach is made possible by the recent installation of a wide-area real-time measurement system based upon Phasor Measurement Unit (PMU) technology. One potential large-scale damping approach is based on energy storage devices. Such an approach has considerable promise for damping oscillations. This paper considers the placement of such devices within the wNAPS system. We explore combining energy storage devices with HVDC modulation of the Pacific DC Intertie (PDCI). We include eigenanalysis of a reduced-order wNAPS system, detailed analysis of a basic two-area dynamic system, and full-order transient simulations. We conclude that the optimal energy storage location is in the area with the lower inertia.

%B 2014 IEEE Power & Energy Society General Meeting %I IEEE %C National Harbor, MD, USA %P 1 - 5 %8 07/2014 %R 10.1109/PESGM.2014.6939875 %0 Conference Paper %B 2013 IEEE Power & Energy Society (PES) General Meeting %D 2013 %T Damping of inter-area oscillations using energy storage %A Jason C. Neely %A Raymond H. Byrne %A Ryan T. Elliott %A Cesar A. Silva-Monroy %A David A. Schoenwald %A Dan Trudnowski %A Matthew K. Donnelly %K AA14-006 %K AARD %K CERTS %K synchrophasor-based control %XLow frequency inter-area oscillations have been identified as a significant problem in utility systems due to the potential for system damage and the resulting restrictions on power transmission over select lines. Previous research has identified real power injection by energy storage based damping control nodes as a promising approach to mitigate inter-area oscillations. In this paper, a candidate energy storage system based on UltraCapacitor technology is evaluated for damping control applications in the Western Electric Coordinating Council (WECC), and an analytical method for ensuring proper stability margins is also presented for inclusion in a future supervisory control algorithm. Dynamic simulations of the WECC were performed to validate the expected system performance. Finally, the Nyquist stability criteria was employed to derive safe operating regions in the gain, time delay space for a simple two-area system to provide guaranteed margins of stability.

%B 2013 IEEE Power & Energy Society (PES) General Meeting %I IEEE %C Vancouver, BC %P 1 - 5 %8 07/2013 %R 10.1109/PESMG.2013.6672775 %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 Conference Paper %B 2013 IEEE Power & Energy Society General Meeting %D 2013 %T PDCI damping control analysis for the western North American power system %A Dan Trudnowski %A Dmitry Kosterev %A John Undrill %K AA14-006 %K AARD %K CERTS %K synchrophasor-based control %XTransmission capacity in the western North American power system (termed the wNAPS) is often limited by poorly-damped electromechanical oscillations. To date, the primary damping controllers applied in the wNAPS are via generator controls using localized feedback signals. Such controls have limited effectiveness for inter-area modes. Recent development of reliable real-time wide-area measurement systems (WAMS) has enabled the potential for large-scale damping control approaches. One such approach is feedback modulation of the Pacific DC Intertie (PDCI). This paper summarizes simulation results from a study to evaluate PDCI damping control in the wNAPS. This includes developing a safe and effective control strategy, quantifying potential improved damping, and conducting open-loop actual-system probing tests.

%B 2013 IEEE Power & Energy Society General Meeting %I IEEE %C Vancouver, BC %P 1 - 5 %8 07/2013 %R 10.1109/PESMG.2013.6672718 %0 Conference Paper %B 2013 IEEE Power & Energy Society (PES) General Meeting %D 2013 %T Some considerations in using Prony analysis to estimate electromechanical modes %A Ning Zhou %A John W. Pierre %A Dan Trudnowski %K AA07-001 %K AARD %K phasor measurement units (PMUs) %XProny analysis has been used to estimate oscillation modes from ringdown responses in a power grid. When applying Prony analysis, several factors must be considered to estimate the modes accurately. In this paper, a general prediction model is proposed for the Prony analysis. The influence of decimation factors, model orders, and linear solvers on estimation accuracy is studied using the Monte Carlo method with a goal of providing a reference for applying Prony analysis to estimate electromechanical modes.

%B 2013 IEEE Power & Energy Society (PES) General Meeting %I IEEE %C Vancouver, BC %P 1 - 5 %8 07/2013 %R 10.1109/PESMG.2013.6672888 %0 Report %D 2012 %T Autonomous Demand Response for Primary Frequency Regulation %A Matthew K. Donnelly %A Mattix, S. %A Dan Trudnowski %A Jeffery E. Dagle %K demand response %K frequency regulation %K Load as a Resource %K LR11-010 %X Demand response has long been an integral part of power system control and operation. Recently, demand response has received more interest as a potentially effective tool to help gain higher levels of asset utilization on the bulk power grid and to avoid or delay the need for new transmission-line construction. Autonomous demand response is defined as load response to system-based signals rather than to master control signals or price signals from a central dispatch center. The most readily available system-based signal is frequency, which can be a very reliable indicator of grid instability, problems, or abnormal conditions. Speed governing systems at central generating stations, when operating in droop mode, employ frequency as the primary feedback signal. These governors are largely responsible for affecting primary frequency response of the bulk power grid thereby maintaining a continuous balance between supply and demand. This research examines the use of autonomous demand response to provide primary frequency response in an interconnected grid. Ultimately, it is conceivable that all primary frequency response might be delivered by responsive load leaving dispatchable generation to be base loaded or ramped with very slow ramp rates. If this objective were to be achieved, numerous benefits might be realized, including reduced emissions from fossil plants as a result of higher operating efficiencies and greater flexibility in integrating variable generation sources such as wind and solar. The work builds on previous studies in several key areas: it uses a large realistic model (i.e., the interconnection of the western United States and Canada); it establishes a set of metrics that can be used to assess the effectiveness of autonomous demand response; and it independently adjusts various parameters associated with using autonomous demand response to assess effectiveness and to examine possible threats or vulnerabilities associated with the technology. Where prior research has focused on showing the efficacy of the concept in delivering primary frequency response, this study’s primary objective was to identify any potential deleterious effects. %I Pacific Northwest National Laboratory %8 01/2012 %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 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 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 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 Report %D 2010 %T MANGO - Modal Analysis for Grid Operation: A Method for Damping Improvements through Operating Point Adjustment %A Zhenyu Huang %A Ruisheng Diao %A Ning Zhou %A Jason C. Fuller %A Francis K. Tuffner %A William A. Mittelstadt %A Yousu Chen %A John F. Hauer %A Dan Trudnowski %A Jeffery E. Dagle %K AA07-001 %K AARD %K advanced measurements and control %K CERTS %XWith more and more phasor measurements available and ModeMeter techniques maturing, there is yet a need for methods to bring modal analysis from monitoring to actions. The methods should be able to associate low damping with grid operating conditions, so operators or automated operation schemes can respond when low damping is observed. The work presented in this report aims to develop such a method and establish a Modal Analysis for Grid Operation (MANGO) procedure to provide recommended actions (such as generation re-dispatch or load reduction), and aid grid operation decision making for mitigating inter-area oscillations. This project directly contributes to the Department of Energy Transmission Reliability Program's goal of "improving reliability of the nation's electricity delivery infrastructure."

%P 92 %8 10/2010 %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 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