Fabian M. Uriarte

A DC Arc Model for Series Faults in Low Voltage Microgrids

This paper presents a dc arc model to simplify the study of a critical issue in dc microgrids: series faults. The model is derived from a hyperbolic approximation of observed arc voltage and current patterns, which permit analyzing the arc in terms of its resistance, power, energy, and quenching condition. Recent faults staged by the authors on a dc microgrid yielded enough data to develop an arc model for three fault types: constant-gap speed, fixed-gap distance, and accelerated gap. The results in this paper compare experimental and simulation results for the three fault types. It is concluded that because the instantaneous voltage, current, power, and energy waveforms produced by the model agree well with experimental results, the model is suitable for transient simulations.

Microgrid Ramp Rates and the Inertial Stability Margin

Variable power sources are becoming increasingly common in low-inertia microgrids. Inadequate amounts, however, can disrupt electric service if ramped events occur too quickly. The authors introduce an approach to predict how long microgrids can withstand ramped events as a function of local inertia. Although microgrids can ride through disturbances using local inertia and other technologies, it is not clear for how long disturbances can be tolerated-particularly when in progress. The estimated reaction times are presented, first, as stability margins to illustrate how ramp-rate magnitudes relate to local inertia. Then, use of the reaction times is demonstrated as a forward-looking capability to anticipate frequency deviation times as a microgrid model undergoes large solar ramp rates. It is shown that the available remaining times can be estimated even as disturbances and remedial actions take place.

Utilization of Optimal Control Law to Size Grid-Level Flywheel Energy Storage

This paper presents a method for sizing grid-level flywheel energy storage systems using optimal control. This method allows the loss dynamics of the flywheel system to be incorporated into the sizing procedure, and allows data-driven trade studies to be performed which trade peak grid power requirements and flywheel storage capacity. A demonstration of the sizing methodology will be illustrated through a case study based on home consumption and solar generation data collected from the largest smart grid in Austin, Texas, USA.

Flexible test bed for MVDC and HFAC electric ship power system architectures for Navy ships

Several power architectures have been considered for Navy ships and significant effort has been focused on simulation of the various power system topologies. The University of Texas at Austin Center for Electromechanics (UT-CEM) has taken a step forward by assembling a microgrid capable of operating at MW power levels to experimentally validate key elements of these system models. The present system is an MVDC architecture but can easily be reconfigured as an HFAC network. This paper describes the UT-CEM microgrid and plans to demonstrate critical technical issues in naval power systems and enable model validation. The intent is for the microgrid to be a flexible test bed for investigation of naval power systems and to become a useful bridge from theoretical and computer studies to a realistic experimental platform.

Development of a multicore power system simulator for ship systems

An important impediment to using widely available software to simulate the behavior of advanced power systems for electric ships is that the simulation time is too long to be practical. Consequently, the Center for Electromechanics at the University of Texas at Austin (UT-CEM) is developing a multicore power system solver to simulate large shipboard power systems. In its first year of development, the focus is on testing CEMs solver (CEMS) for accuracy. This paper presents an overview of the major traits of CEMS, and compares its simulation results to the well-known commercial power system simulator SimPowerSystems. Preliminary results show that accuracy is maintained and improved in specific test cases.

Multicore simulation of an AC-radial Shipboard Power System

This work presents an approach to parallelize the simulation of AC-Radial Shipboard Power Systems (SPSs) on multicore computers. Time domain simulations of SPSs are notoriously slow due to the order of SPSs and the presence of time-varying component models. A common approach to reduce simulation run-time is to partition power systems using Bergerons travelling-wave model and to simulate the subsystems on a distributed computer. In this work a SPS is partitioned along cable capacitor loops using a diakoptics-based approach and the simulation conducted on a quad-core computer. A case study is presented that empirically determines a good number of SPS partitions for a multithreaded simulation, such that the speed gain is maximal and accuracy is preserved.

Diakoptics in Shipboard Power System Simulation

A partitioning scheme for transient simulation of shipboard power systems (SPS) is presented. Using diakoptics, the piecewise transient solution to a ungrounded AC-radial (3phi) ring-bus system is found. Cable tie-lines (floating pi-segments) on the SPS ring are converted to hexagon equivalents by discretization and decoupled via source-transportation, diakoptics, and exploiting mutual-susceptance links. Transient simulation results from circuit simulation (as a whole) and via diakoptics (piecewise) are compared and discussed.

Real-Time Simulation using PC-based Kernels

National Instruments and The MathWorks, Inc. make PC real-time simulation possible with the use of real-time kernels. In this work, a small three-phase radial power system is modeled and simulated using these real-time environments to determine the feasibility, accuracy, and determinism of boot-loaders as an alternative to costly real-time simulators for smaller systems. Implications and modeling methodologies of simulating the power system in real-time using PCs are discussed providing a discussion at the end comparing both products for the interested public

Effects of high penetration levels of residential photovoltaic generation: Observations from field data

Photovoltaic (PV) generation technologies, often deemed a viable solution for reducing greenhouse gases and decreasing electricity demand, have become increasingly prevalent in their deployment. Particular progress in their implementation has been evidenced in residential areas characterized by rooftop-mounted PV arrays. Aside from the known advantages provided by residential PV generation, one noteworthy disadvantage confronting the electric utility is the degradation of power factor when grid-tied PV sources are extensively integrated into the electrical distribution system. In this paper, the effect of PV sources on power factor is studied using recorded field data from a residential community that is part of a large-scale smart grid demonstration project in Austin, Texas.

A Tensor Approach to the Mesh Resistance Matrix

This paper presents a tensor approach to obtain the mesh resistance matrix of a power system. The traditional approach to the mesh matrices naturally relates to graph theory, where the fundamental loops of a representative graph are found from a spanning tree. While valid, mesh identification is time consuming, involves unnecessary programming overhead, yields dense mesh matrices, and requires developing good search heuristics. The proposed approach uses a connection tensor to form a sparse mesh resistance matrix without resorting to graph theory. It allows for the interconnection of only those meshes circulating around the terminals of each power apparatus, which is more effective than searching for the meshes of an entire power system. Detailed steps to form the tensor and supporting examples illustrate the procedure presented in several scenarios. It is also shown that the mesh resistance matrix is sparse and that the computational effort to form the tensor is negligible.