Date of Graduation
Master of Science in Electrical Engineering (MSEE)
Juan C Balda
Second Committee Member
There is a rising number of inverter-based resources (IBRs) being integrated with distribution systems are becoming a more common occurrence. With integration of IBRs inverters, power utilities are experiencing an increase of number of operations with regards to voltage and frequency support. To maintain grid stability and reliability, IBRs need to provide some of the services currently (or formerly) provided by synchronous generators. Interconnection standards, like the IEEE 1547. 2018 has include requirements for IBRs to have the capability to provide some of these services—such as frequency and voltage support—and the procurement and deployment of the services can be implemented either as mandatory interconnection requirements or as market products. All the IBRs deployed today are grid-following (GFL), and read the voltage and frequency of the grid and inject current to provide the appropriate amount of active and reactive power. The fundamental GFL IBR design assumption is that there are still enough synchronous generators on the grid to provide a relatively strong and stable voltage and frequency signal, which GFL IBRs can “follow.” But since levels of GFL are increasing, there will be a limit to how far GFL controls can be pushed, and, at some point, new advanced inverter controls (termed grid forming (GFM)) will be needed to maintain system stability. GFM IBRs will also be needed to establish voltage and frequency during operating conditions when there are zero synchronous machines (100 percent IBR penetration). Power systems around the world are at the point of now needing to make this technological leap; however, system operators and planners, equipment owners, and manufacturers today are facing a circular problem regarding the deployment of advanced IBR controls. Which comes first, the requirement for a capability or the capability itself? How do grid operators know what performance or capability is possible from new equipment (and therefore what they could require)? How can they evaluate costs and benefits of having such equipment on the grid? What drives manufacturers to invest in modern technology without its being mandated for interconnection to the grid or otherwise incentivized by the market? The objective of this thesis is to provide a better understanding of ride through fault capabilities of Grid Forming Inverter (GFM) tied into the generation side of the power grid when using control functions. Furthermore, to investigate the robustness of implementing time delay with a PLL system within the control settings for grid forming inverters. To this end, to identify the contributing factors that affects the stability of the time delay to better design and future models of GFMs. As discussed, the microgrid is a potential solution for future distributed generation systems. However, controlling a microgrid is still a complex issue and many proposed solutions, are only based on locally measured signals without any communications; thus, it is difficult to achieve global optimization. Future works on this topic will analyse the role of restoration practices, communication control techniques to better approximate the delay. The specific areas below will be discussed in this thesis.
Hepburn, K. (2023). Modeling & Small Signal Analysis of Grid Forming Inverter. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/4848