Shrirang Abhyankar

Interfacing Issues in Multiagent Simulation for Smart Grid Applications

This paper discusses design and application of the multiagent simulation technology aiming to meet smart grid requirements. The difference between multiagent systems and multiagent simulation in smart grid applications is clarified. The state-of-the-art applications of multiagent simulation in power and energy systems are classified based on the simulation environment. The paper also addresses the interface issues including synchronization and data distribution for multiagent co-simulation. In addition, the emerging research paradigms in smart grid multiagent simulation are identified.

An implicitly-coupled solution approach for combined electromechanical and electromagnetic transients simulation

This paper presents a novel implicitly-coupled solution approach for the combined electromechanical and electromagnetic transients simulation. Unlike the existing hybrid simulators that use an explicit approach to interface separate transient stability (TS) and electromagnetic transients (EMT) programs, the authors propose combining the equations of the two simulators and solving them simultaneously by an implicit approach. To combine the two sets of equations with their different time steps, and ensure that the TS and EMT solutions are consistent, the equations for TS and coupled-in-time EMT equations are solved simultaneously, referred to as TSEMT simulation. The simulation results for the proposed implicitly-coupled solution approach on the WECC 9-bus system are discussed. Along with the implicitly-coupled solution approach, a novel strategy, referred to as TS3ph-TSEMT, based on difference between the phasor boundary bus voltages of the detailed and external systems is also proposed to terminate the implicitly-coupled TSEMT simulation and continue with only the TS simulation. The computational efficiency of the proposed TS3ph-TSEMT approach is presented for the 9-bus and 118-bus systems.

Real-Time Power System Dynamics Simulation Using a Parallel Block-Jacobi Preconditioned Newton-GMRES Scheme

Real-time dynamics simulation of large-scale power systems is a computational challenge because of the need to solve a large set of stiff, nonlinear differential-algebraic equations. The main bottleneck in these simulations is the solution of the linear system during each nonlinear iteration of Newtons method. We present a parallel linear solution scheme using the Krylov subspace-based iterative solver GMRES with a BlockJacobi preconditioner. The scheme shows promise for real-time dynamics simulation, with a good speed up for a 2383-bus, 327-generator test case. Results obtained for both stable and unstable operating conditions show that real-time simulation speed can be realized by using the proposed parallel linear solution scheme.

Implicitly Coupled Electromechanical and Electromagnetic Transient Analysis Using a Frequency-Dependent Network Equivalent

This paper presents an improved solution of the implicitly coupled electromechanical and electromagnetic transient analysis problem using a frequency-dependent network equivalent (FDNE). In previous work, the fundamental frequency equivalent was used as the network equivalent of the external system. While simple, this fundamental frequency equivalent is only accurate for a single frequency, the fundamental frequency. This may lead to an inaccurate equivalent of the transient stability (TS) network. This paper extends previous work by using an FDNE derived from the vector-fitting technique. The FDNE is able to resolve the transient behavior over a wider frequency spectrum leading to a more accurate representation of the TS network. Results demonstrating the accuracy of the proposed scheme are presented on a 3-bus test system and the IEEE 118-bus system.

Dynamic security constrained optimal power flow using finite difference sensitivities

We present a novel technique for determining the solution of optimal power flow, including dynamic security constraints, using forward sensitivities computed by using finite differences. Finite differencing provides an easy way of computing the sensitivities of the dynamic security constraints in optimal power flow. A dynamic security measure based on the frequency excursion of the generators is presented. Our formulation also yields the marginal cost associated with the generators frequency excursion.

Discrete Adjoint Sensitivity Analysis of Hybrid Dynamical Systems With Switching

Sensitivity analysis is an important tool for describing power system dynamic behavior in response to parameter variations. It is a central component in preventive and corrective control applications. The existing approaches for sensitivity calculations, namely, finite-difference and forward sensitivity analysis, require a computational effort that increases linearly with the number of sensitivity parameters. In this paper, we investigate, implement, and test a discrete adjoint sensitivity approach whose computational effort is effectively independent of the number of sensitivity parameters. The proposed approach is highly efficient for calculating sensitivities of larger systems and is consistent, within machine precision, with the function whose sensitivity we are seeking. This is an essential feature for use in optimization applications. Moreover, our approach includes a consistent treatment of systems with switching, such as dc exciters, by deriving and implementing the adjoint jump conditions that arise from state-dependent and time-dependent switchings. The accuracy and the computational efficiency of the proposed approach are demonstrated in comparison with the forward sensitivity analysis approach. This paper focuses primarily on the power system dynamics, but the approach is general and can be applied to hybrid dynamical systems in a broader range of fields.

Evaluation of overlapping restricted additive schwarz preconditioning for parallel solution of very large power flow problems

The computational bottleneck for large nonlinear AC power flow problems using Newtons method is the solution of the linear system at each iteration. We present a parallel linear solution scheme using the Krylov subspace-based iterative solver GMRES preconditioned with overlapping restricted additive Schwarz method (RASM) that shows promising speedup for this linear system solution. This paper evaluates the performance of RASM with different amounts of overlap and presents its scalability and convergence behavior for three large power flow problems consisting of 22,996, 51,741, and 91,984 buses respectively.

Equivalent models for implicitly-coupled electromechanical and electromagnetic transient analysis

This paper presents two sets of equivalent models for implicitly-coupled electromechanical and electromagnetic transient analysis: a Thevenin equivalent of the electromechanical network and a Norton equivalent of the electromechanical network. Due to the possible lack of voltage reference in the electromagnetic network, the Norton equivalent of the electromechanical network is not as robust as the Thevenin equivalent in implicitly-coupled transient simulation. Results demonstrating the advantage of the implicitly-coupled electromechanical and electromagnetic simulator with Thevenin equivalent of the electromechanical network are presented for a 3 bus test system.

Modeling of transmission line faults for transient stability analysis

This paper presents a novel approach to model faults on transmission lines for power system transient stability studies. Typically such faults, incident at a certain distance along a transmission line, are modeled by the introduction of dummy or fictitious buses. This dummy bus is placed at the length along the transmission line at which the fault is incident and the fault is applied on it. The introduction of dummy buses introduces inefficiencies in the solution process, particularly from a computational view point due to the need of resizing of the vectors and matrices. In this paper, we present a direct approach for modeling that avoids the need of dummy buses. We derive the necessary equations representing the impact of transmission line faults on the buses connected to the transmission line. The impact of such a fault is then modeled by mere modification of the elements of system admittance matrix. Numerical results on test systems are presented comparing its accuracy with a commercial software.

Guest Editorial High Performance Computing (HPC) Applications for a More Resilient and Efficient Power Grid

The power grid has been evolving over the last 120 years, but it is seeing more changes in this decade and next than it has seen over the past century. In particular, the widespread deployment of intermittent renewable generation, smart loads and devices, hierarchical and distributed control technologies, phasor measurement units, energy storage, and widespread usage of electric vehicles will require fundamental changes in methods and tools for the operation and planning of the power grid. The resulting new dynamic and stochastic behaviors will demand the inclusion of more complexity in modeling the power grid. Solving such complex models in the traditional computing environment will be a major challenge. Along with the increasing complexity of power system models, the increasing complexity of smart grid data further adds to the prevailing challenges. In this environment, the myriad of smart sensors and meters in the power grid increase by multiple orders of magnitude, so do the volume and speed of the data. The information infrastructure will need to drastically change to support the exchange of enormous amounts of data as smart grid applications will need the capability to collect, assimilate, analyze and process the data, to meet real-time grid functions. High performance computing (HPC) holds the promise to enhance these functions, but it is a great resource that has not been fully explored and adopted for the power grid domain.