Virtual Synchronous Machine functionality in Voltage Source Converter: Control and design requirements

The AC transmission grid constitutes the backbone of the renewable energy revolution, driving the reduction in carbon emissions from power generation. The stability of the AC grid, traditionally maintained by large moments of inertia provided by traditional synchronous generators, increasingly calls for new frequency support mechanisms since these synchronous generators are being supplanted by new intermittent, power electronics-interfaced renewable energy sources. Network operators are thus examining the integration of new actors, e.g. HVDC converters and storage assets, to provide additional ancillary services such as Enhanced and Future Frequency Response. These actors will be contracted to provide frequency response in 1 second or less before secondary response takes over. HVDC converters represent the ideal candidate for providing this type of ancillary services as they constitute some of the highest rated assets in the grid. However, equipping HVDC converters with VSM or grid forming functionalities requires extensive rethink of their control algorithm, potentially also impacting all the power components due the extra power rating.

This project will examine the integration, through control and design improvements, of Virtual Synchronous Machine (VSM) functionality within existing and future HVDC power converters; tapping into their deep interaction with the AC grid to provide both inertia response and grid forming functionalities. This would increase the stability of the AC transmission grid in time for higher penetration of renewable energy sources. This project is supported by the Energy Technology Partnership Scotland (ETP) and GE Grid Solutions, a leading HVDC converter manufacturer, and will be hosted at the School of Engineering of the University of Edinburgh.

The PhD study will start by surveying the literature about VSM and implement a control algorithm enabling VSM in an MMC (Year 1), then studying the hardware implication of VSM in terms of overrating of existing power devices and possible integration of energy storage devices (Year 2), and finally test all these elements together in a lab-scale HVDC converter to support these findings with hardware results (Year 3). A one-month visit hosted at GE Grid Solutions in Stafford will also take place at some point during the PhD project to provide essential industry exposure to the researcher.