Publications

Limited access to transmission lines after a major contingency event can inhibit restoration efforts. After Hurricane Maria, for example, flooding and landslides damaged roads and thus limited travel. Transmission lines are also often situated far from maintained roadways, further limiting the ability to access and repair them. Therefore, this paper proposes a methodology for assessing Puerto Rico’s infrastructure (i.e., roads and transmission lines) to identify potentially hard to reach areas due to natural risks or distance to roads. The approach uses geographic information system (GIS) data to define vulnerable areas, that may experience excessive restoration times. The methodology also uses graph theory analysis to find transmission lines with high centrality (or importance). Comparison of these important transmission lines with the vulnerability results found that many reside near roads that are at risk for landslides or floods.

In this paper, the development of a mathematical model for islanding detection method based on the concept of a digital twin is presented. The model estimates the grid impedance seen by a distributed energy resource. The proposed algorithm has characteristics of passive and active islanding detection methods. Using a discrete state-space representation of a dq0 axis power system as equality constraints, a digital twin is optimized to match the power system of interest. The concept is to use the estimated grid impedance as the parameter to identify the difference between normal operation and islanding scenarios. Selecting arbitrary initial values, the digital twin approximates the response of the actual system and therefore a value for the system impedance. Results indicate that the proposed method has the potential to estimate the grid impedance at the point of common coupling.

Due to the increased penetration in Distributed Energy Resources (DERs), especially in Photovoltaic (PV) systems, voltage and frequency regulation has become a topic of interest. Utilities have been requesting DER voltage and frequency support for almost two decades. Their request was addressed by standards such as the IEEE Std 1547-2018. With the continuous improvements in inverters' ability to control their output voltage, power, and frequency, a group of advanced techniques to support the grid is now required by the interconnection standard. These techniques are known as Grid Support Functions (GSF), and they allow the inverter to provide voltage and frequency support to the grid as well as the ability to ride-through abnormal events. Understanding how a GSF behaves is challenging, especially when multiple GSFs are combined to help the utility to control the system voltage and frequency. This paper evaluates the effects of GSF's on the IEEE Std 1547.1-2020 Unintentional Islanding Test 5B by comparing simulation results from a developed PV inverter model and experimental results from a Power Hardware-in-the-Loop platform.

DC microgrids envisioned with high bandwidth communications may well expand their application range by considering autonomous strategies as resiliency contingencies. In most cases, these strategies are based on the droop control method, seeking low voltage regulation and proportional load sharing. Control challenges arise when coordinating the output of multiple DC microgrids composed of several Distributed Energy Resources. This paper proposes an autonomous control strategy for transactional converters when multiple DC microgrids are connected through a common bus. The control seeks to match the external bus voltage with the internal bus voltage balancing power. Three case scenarios are considered: standalone operation of each DC microgrid, excess generation, and generation deficit in one DC microgrid. Results using Sandia National Laboratories Secure Scalable Microgrid Simulink library, and models developed in MATLAB are compared.