This paper presents a strategy to implement transient stability constrained optimal power flow in cascading outages. Anticipatory computing detects transient instability due to weakened system conditions in cascading progressions and prepares transient stability constraints for optimal power flow. The prepared constraints use trajectory sensitivities, which can speed up the analysis by estimating rotor angle response changing with generation levels. The proposed strategy has been tested on a 140-bus, 48-machine system.

%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.2014.6939917 %0 Journal Article %J IEEE Transactions on Power Systems %D 2013 %T A Computational Strategy to Solve Preventive Risk-Based Security-Constrained OPF %A Wang, Qin %A James D. McCalley %A Zheng, Tongxin %A Litvinov, Eugene %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K CERTS %K power system security %K RTGRM %K System Security Tools %X The benefit of risk-based (RB) security-constrained optimal power flow (SCOPF) model lies in its ability to improve the economic performance of a power system while enhancing the system's overall security level. However, the RB-SCOPF model is difficult to solve due to the following two characteristics: 1) the overload severity of a circuit changes with the loading condition on it, thus is hard to express with a deterministic function, and 2) the risk index is a function of the state variables in both normal and contingency states, which greatly increases the scale of optimization. To handle the first issue, a new expression of severity function is proposed so that it is possible to decompose the model into a SCOPF subproblem and a risk subproblem. To deal with the second issue, a nested Benders decomposition with multi-layer linear programming method is proposed. Illustrations use the ISO New England bulk system is provided to demonstrate the feasibility of the proposed method. Analysis is presented to demonstrate the merits of the RB-SCOPF over the traditional SCOPF model. %B IEEE Transactions on Power Systems %V 28 %P 1666 - 1675 %8 05/2013 %N 2 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2012.2219080 %0 Book Section %B High Performance Computing in Power and Energy Systems %D 2013 %T Dynamic Load Balancing and Scheduling for Parallel Power System Dynamic Contingency Analysis %A Siddhartha Kumar Khaitan %A James D. McCalley %K AA09-001 %K AARD %K Automatic Switchable Network (ASN) %K PSERC %X Power system simulations involving solution of thousands of stiff differential and algebraic equations (DAE) are extremely computationally intensive and yet crucial for grid security and reliability. Online simulation of minutes to hours for a large number of contingencies requires computational efficiency several orders of magnitude greater than what is todays state-of-the-art. We have developed an optimized simulator for single contingency analysis using efficient numerical algorithms implementation for solving DAE, and scaled it up for large-scale contingency analysis using MPI. A prototype parallel high speed extended term simulator (HSET) on in-house high performance computing (HPC) resources at Iowa State University (ISU) (namely Cystorm Supercomputer) is being developed. Since the simulation times across contingencies vary considerably, we have focused our efforts towards development of efficient scheduling algorithms through work stealing for maximal resource utilization and minimum overhead to perform faster than real time analysis. This chapter introduces a novel implementation of dynamic load balancing algorithm for dynamic contingency analysis. Results indicate potential for significant improvements over the state-of-the-art methods especially master-slave based load balancing typically used in power system community. Simulations of thousands of contingencies on a large real system were conducted and computational savings and scalability results are reported. %B High Performance Computing in Power and Energy Systems %I Springer Berlin Heidelberg %C Berlin, Heidelberg %P 189 - 209 %@ 978-3-642-32682-0 %R 10.1007/978-3-642-32683-7_6 %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 IEEE Power & Energy Society General Meeting %D 2013 %T Parallelizing power system contingency analysis using D programming language %A Siddhartha Kumar Khaitan %A James D. McCalley %K AA09-001 %K RTGRM %K System Security Tools %XTo ensure security, analyzing a large number of contingencies is important, which requires use of parallel computing resources. In this paper, we present an approach for parallelization and load balancing of contingency analysis (CA) in power systems using D programming language. We parallelize CA using a multicore processor and and propose and employ work-stealing based efficient scheduling to achieve load-balancing. We evaluate the features of D which are important for parallelization of CA and obtaining large performance gains. Our approach promotes legacy code reuse and hence is suitable for modern control centers which cannot afford porting their legacy code to other high-performance computing (HPC) platforms. We have conducted time domain simulation using a large 13029-bus test system with hundreds of contingencies and parallelized CA over 2, 4, 8, 12 and 16 cores. The results have confirmed that our approach outperforms a conventional scheduling technique and also offers large computational savings over serial execution.

%B 2013 IEEE Power & Energy Society General Meeting %I IEEE %C Vancouver, BC %P 1 - 5 %8 07/2013 %R 10.1109/PESMG.2013.6672115 %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 2013 %T Risk and “N-1” Criteria Coordination for Real-Time Operations %A Wang, Qin %A James D. McCalley %K AA09-001 %K AARD %K RTGRM %K System Security Tools %X This letter describes a new perspective on coordinating system “N-1” criteria and risk for real-time operations, where risk is modeled to capture the system's overall security level. A risk-based security-constrained optimal power flow (RB-SCOPF), considering “N-1” criteria and risk together, is compared with the traditional SCOPF. The IEEE 30-bus system is tested to illustrate the coordination between risk and “N-1” criteria in RB-SCOPF. %B IEEE Transactions on Power Systems %V 28 %P 3505 - 3506 %8 08/2013 %N 3 %! IEEE Trans. Power Syst. %R 10.1109/TPWRS.2013.2258820 %0 Conference Paper %B 2013 IEEE Power & Energy Society General Meeting %D 2013 %T Trajectory sensitivities: Applications in power systems and estimation accuracy refinement %A Lei Tang %A James D. McCalley %K AA09-001 %K RTGRM %XThis paper first briefly summarizes the stat-of-the-art work of trajectory sensitivity applications in various areas of power systems. Through linearizing the system along the nominal trajectories, trajectory sensitivities can estimate the trajectory deviations after small parameter change, but will inevitably cause estimation error due to system nonlinearity. Two strategies are proposed in this paper to refine the estimation accuracy in situations when the error is unacceptable. These two strategies are second order trajectory sensitivities and switching operating states method. The two strategies have been tested on New England 39-bus system. The results prove their validity.

%B 2013 IEEE Power & Energy Society General Meeting %I IEEE %C Vancouver, BC %P 1 - 5 %8 07/2013 %R 10.1109/PESMG.2013.6672533 %0 Conference Paper %B 2012 North American Power Symposium (NAPS) %D 2012 %T An efficient transient stability constrained optimal power flow using trajectory sensitivity %A Lei Tang %A James D. McCalley %K AA09-001 %K optimal power flow (OPF) %K RTGRM %K System Security Tools %XA well-structured two-step efficient transient stability constrained optimal power flow is proposed. The transient stability constraints are obtained through time domain simulation and its corresponding trajectory sensitivity calculation. The process to obtain the constraints is an independent step from the dispatch problem solving. The added transient stability constraints prevent first swing instability, and bring much less computational burden than steady state security constraints. The proposed method was tested on a 9-bus system and the New England 39-bus system.

%B 2012 North American Power Symposium (NAPS) %I IEEE %C Champaign, IL, USA %P 1 - 6 %8 09/2012 %@ 978-1-4673-2306-2 %R 10.1109/NAPS.2012.6336308 %0 Conference Paper %B 2012 SC Companion: High Performance Computing, Networking, Storage and Analysis (SCC) %D 2012 %T EmPower: An Efficient Load Balancing Approach for Massive Dynamic Contingency Analysis in Power Systems %A Siddhartha Kumar Khaitan %A James D. McCalley %K AA09-001 %K RTGRM %K System Security Tools %XPower system simulations involving solution of thousands of stiff differential and algebraic equations (DAE) are computationally intensive and yet crucial for grid security and reliability. Online simulations of a large number of contingencies require very high computational efficiency. Furthermore, since the simulation times across the contingencies vary considerably, dynamic load balancing of parallel contingency analysis (CA) is required to ensure maximum resource utilization. However, the state-of-the-art contingency analysis techniques fail to fulfill this requirement. In this paper, we present EmPower, an Efficient load balancing approach for massive dynamic contingency analysis in Power systems. For single contingency analysis, EmPower uses time domain simulations and incorporates efficient numerical algorithms for solving the DAE. Further, the contingency analysis approach is scaled for large scale contingency analysis using MPI based parallelization. For enabling an efficient, non-blocking implementation of work-stealing, multithreading is employed within each processor. Simulations of thousands of contingencies on a supercomputer have been performed and the results show the effectiveness of EmPower in providing good scalability and huge computational savings.

%B 2012 SC Companion: High Performance Computing, Networking, Storage and Analysis (SCC) %I IEEE %C Salt Lake City, UT %P 289 - 298 %8 11/2012 %@ 978-1-4673-6218-4 %R 10.1109/SC.Companion.2012.47 %0 Journal Article %J Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability %D 2012 %T Long-term benefits of online risk-based direct-current optimal power flow %A Dai, R.-C. %A Pham, H. %A Wang, Y. %A James D. McCalley %K AA09-001 %K AARD %K CERTS %K optimal power flow (OPF) %K RTGRM %K System Security Tools %X An online operational risk management method is presented in this paper. In this method, a risk-based direct-current (DC) optimal power flow approach is utilized to replace a traditional security-constrained DC optimal power flow approach. This risk management method is integrated into a commercial energy management system/dispatcher training simulator system to monitor and control system operation risk online. Comparison of the approach with traditional security assessment shows significant benefits over the long term via cost reduction and risk mitigation. A case study provides supporting evidence of risk mitigation in terms of steady-state angular separation reduction and cascading prevention. %B Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability %V 226 %P 65 - 74 %8 02/2012 %N 1 %! Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability %R 10.1177/1748006X11433660 %0 Conference Paper %B 2012 SC Companion: High Performance Computing, Networking, Storage and Analysis (SCC) %D 2012 %T TDPSS: A Scalable Time Domain Power System Simulator for Dynamic Security Assessment %A Siddhartha Kumar Khaitan %A James D. McCalley %K AA09-001 %K RTGRM %K System Security Tools %XSimulation plays a very crucial role to model, study and experiment with any design innovation proposed in the power systems. Since mathematical modeling of power systems leads to tens of thousands of stiff DAEs (differential and algebraic equations), the design of power system simulators involve exercising a trade-off between the simulation speed and modeling accuracy. Lack of efficient and detailed simulators forces the designers to experiment their techniques with small test systems and hence, the results obtained from such experiments may not be representative of the results obtained using real-life power systems. In this paper, we present TDPSS, a high speed time domain power system simulator for dynamic security assessment. TDPSS has been designed using object-oriented programming framework, and thus, it is modular and extensible. By offering a variety of models of power system components and fast numerical algorithms, it provides the user with the flexibility to experiment with different design options in an efficient manner. We discuss the design of TDPSS to give insights into the simulation infrastructure and also discuss the areas where TDPSS can be extended for parallel contingency analysis. We also validate it against the commercial power system simulators, namely PSSE and DSA Tools. Further, we compare the simulation speed of TPDSS for different numerical algorithms. The results have shown that TDPSS is accurate and also outperforms the commonly used commercial simulator PSSE in terms of its computational efficiency. .

%B 2012 SC Companion: High Performance Computing, Networking, Storage and Analysis (SCC) %I IEEE %C Salt Lake City, UT %P 323 - 332 %8 11/2012 %@ 978-1-4673-6218-4 %R 10.1109/SC.Companion.2012.51 %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 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 Conference Paper %B 2009 IEEE/PES Power Systems Conference and Exposition (PSCE) %D 2009 %T Fast parallelized algorithms for on-line extended-term dynamic cascading analysis %A Siddhartha Kumar Khaitan %A Chuan Fu %A James D. McCalley %K AA09-001 %K Power system dynamics %K RTGRM %X Very fast on-line computational capability to predict mid-term dynamic system response to disturbances and identify corrective actions is an important attribute of high-speed extended term (HSET) time domain simulation (TDS). Focusing on the development of computational speed, this paper propose a parallel strategy intended for deployment on the super computer, Blue Gene/L, to simulate the power system dynamics, which can be described as a set of differential algebraic equations (DAEs). To deal with DAE stiffness problems and fully capture benefits of explicit and implicit integration methods, the partition algorithm called recursive projection method (RPM) is employed. Additionally, good load balancing for parallel computation is achieved using waveform relaxation method (WRM) to separate the stiff parts of DAE. Multi-frontal massively parallel sparse direct solver (MUMPS) is utilized to solve the linear systems involved in the implicit methods. This paper reports on the design. %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.2009.4840238 %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 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 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