Grid Forming Converter Controller Design And Response to Disturbances and Faults in a Power System with Low Synchronous Generation

  • Panagiotis Marinakis

Student thesis: Doctoral Thesis


Environmental issues, in particular CO2 reduction, is fostering penetration of renewable energy sources (RESs) in many power systems around the world. However, this RES generation has raised concerns about the efficiency, reliability, and cost-effectiveness of electrical power systems. The currently used technology of renewable generation is mainly power electronic, converter-based, via so called grid following control. This technology is well known and can operate well when it is connected in a stiff grid dominated by synchronous generators (SGs). However, their performance is questioned when the SGs are replaced and the main interface of energy is via Non-Synchronous Generators (NSGs), like the majority of the RESs. Further, stability issues also arise that potentially limit the percentage of RES into the power grid. An alternative way to control RES, connected to the grid through power electronics, is with a grid forming converter and associated controller, that would not need to rely on another source to form the system reference voltage and frequency. For the purposes of this thesis such a controller is developed, examined and simulated in Electromagnetic Transient (EMT) studies and the controller impact on system stability is reported. The purpose of the thesis is to examine the behavior of the system during transient periods when it is dominated by grid forming converter-based generation. The grid forming idea has been mainly studied in microgrids. In this thesis the focus is on large power systems. The proposed grid forming converter is able to provide balanced or unbalanced response as necessary. The absence of SGs in the grid would mean that power electronics-based generation should replace the SG features. The impact of grid forming converters on power system strength is addressed. It is known that grid following converters cannot operate sufficiently in weak systems, contrary to grid forming converters. Grid following converters reduce system strength. However, the impact of grid forming converters is not fully understood nor documented, and this is a point where this thesis focuses. The ability of the system to operate sufficiently and smoothly after large system splits is examined. The grid following converters could not survive a system split if they end up in a sub-system with no SG. However, as the penetration of RES increases drastically, it is possible areas of the grid will not have SGs after a split. Hence, the location of grid forming RESs could be crucial for the stability of the system. In this thesis a way to choose the right location for grid forming converter-based generation in a power system with mix of grid forming and grid following converters is also examined.
Date of Award25 Jan 2024
Original languageEnglish
SupervisorNigel Schofield (Main Supervisor)

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