Date of Award
Master of Science (MS)
The development of the synchronous generator in the late 19th century was a catalyst for the energy revolution of the 20th century. Charles Fortescue's paper demonstrating that unbalanced phasors could be expressed as a symmetrical set of balanced phasors was the match that lit the fire of this energy revolution. This paper is regarded as the one of the most important papers written in the 20th century and it has laid the foundation for how every single utility in the world performs fault analysis. The underlying assumptions in this analysis are that the faulted system is linear, which means sources can be represented by a Thevenin model. And secondly, load currents can be neglected compared with fault currents. However, times are changing, and so must our methods of fault analysis.
Over the past 30 years the price of fossil fuels, climate change awareness, and efficiency of non-conventional methods of generation such as wind and solar have all increased drastically. This paired with progressive policymaking using tax breaks and renewable quotas, has begun another revolution in the power industry. Wind and solar are growing at an accelerating rate and this growth is causing waves amongst utilities. These resources use inverters to create AC waveforms on the grid. The primary problem with the proliferation of inverter-based resources is that almost all of them limit the amount of current they can output during a fault scenario to protect their internal components such as MOSFETs and IGBTs. In addition, most inverters connecting solar generators and Type IV wind turbine generators block negative sequence currents. This means an inverter-based resource (IBR) cannot be modeled as a linear source. Due to the low fault contribution, the practice of neglecting load currents in fault analysis also comes under scrutiny.
As IBRs reach higher rates of penetration (and in the case of certain microgrids, 100% penetration) traditional ways of carrying out fault analysis and standard protection schemes will prove to be incapable of achieving their performance objectives. This research will focus on developing new ways to perform fault analysis by using an iterative method to accommodate the behavior of nonlinear sources. The approach will be based on recommendations developed by Working Group C24 of the IEEE Power System Relaying and Control Committee (PSRCC) . The approach uses linearization of the output characteristics of IBRs over a range of terminal voltages provided by the manufacturer, which allows for control-agnostic modeling. Results will be validated with the same system simulated in electromagnetic transient program (EMTP), using PSCAD software.
Greenwood, Austin, "Performing Steady State Fault Analysis in the Phasor Domain Using Inverter Based Resources" (2020). All Theses. 3453.