A Framework for Future Power Systems

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Worldwide, electrical power generation is predominantly through legacy power plants that use conventional turbine-generator (TG) units. The environmental issues and green-house gas emissions associated with the fossil-fueled power plants and the ongoing increase in  demand for the electrical energy indicate continuous increase in the penetration of renewables, e.g., wind and solar-PV power plants, in the power grid. In the future, even most of the legacy fossil-fuel TG-based generation units will be replaced by renewables as they approach the end of their life-spans. Thus, inevitably the penetration-depth of renewables will gradually and continuously increase and eventually the grid will be supplied close to or even at 100% by renewables. In contrast to the conventional TG units which are directly connected to the grid, the common characteristic of renewable generation units is that they are converter-interfaced (CI) units, i.e., connected to the grid by electronic converters. Furthermore, many other subsystems and apparatus within the grid, e.g., high-voltage direct-current (HVDC) converter stations, energy storage units, and reactive power compensators, are also CI units. Thus, in the long run, the ratio of electric power handled by CI units to the power generated by TG units in a grid will substantially increase and consequently the operation, control and protection requirements of the grid will be dictated by the CI units. This trend entails a major departure from the current operation, control, and protection strategies of the existing legacy grid which have been developed within the past several decades based on the characteristics of TG units, and therefore can neither best utilize the features of CI units, guarantee stability, nor security of the future grid under high penetration of CI units. These concerns although acknowledged by stakeholders, have been neither fully understood, investigated, nor formulated, and thus no systematic solutions and remedial measures have been developed. The legacy grid's asset which has been developed in the past several decades is worth billions of dollars. Thus the existing grid cannot be dismantled and replaced by a new grid based on the characteristics of CI units. Therefore, there is a need to develop operation, control, and protection strategies to dynamically accommodate and adapt to the continuous evolution of the legacy grid as the penetration of CI units increases. The R&D focus of this grant application is on the system-level controls of the future grid. The research objectives are to i) develop models for analytical and off-line/real-time simulation tools to investigate and reveal the nature of the dynamic phenomena of the future grid, ii) develop control strategies that can adapt to the evolving grid complexities and systematically address stability issues, and iii) enable best asset utilization of the grid as the penetration of CI units increases.