Impact of Inverter Control on the Dynamic Performance of Power Systems with High Penetration of Inverter-based Resources

The electric power grid is facing major changes due to increasing penetration of inverter-based resources (IBRs) such as solar photovoltaic and wind power. Many power systems around the world are encountering high levels of instantaneous inverter penetration. IBRs have fundamentally different dynamics compared to traditional generators, which can significantly affect the power system dynamic performance at higher penetration levels. Most existing IBRs were originally designed to operate in a stiff network provided by generators that maintain a stiff voltage and frequency. These IBRs are classified as grid-following (GFL) sources, i.e., sources that regulate their power output by measuring and following the angle of the grid voltage using a phase-locked loop (PLL). With a shrinking inventory of conventional generators, there are fewer sources that can sustain stiff voltage and frequency, which can significantly affect the system performance. In contrast, grid-forming (GFM) control of IBRs offers significant advantages over their grid-following counterparts since they can operate as independent voltage sources and actively control the source frequency without depending on the grid frequency. While this control approach is common in microgrid applications, the applicability of this control approach to a larger power system has received little attention to date. The objective of this research program is to investigate the impact of inverter control schemes on the dynamic performance of power systems with a high penetration of IBRs. Different aspects of dynamic performance are investigated – frequency dynamic performance, electromechanical dynamics, voltage stability, and transient stability. Reducing the mechanical inertia of the power system due to transitions from synchronous generators to IBRs is raising fears among grid operators about reliability. The reduction in stored energy in spinning rotors increases the risk of creating larger frequency swings during disturbances that can trip loads or IBRs. The frequency support capabilities of inverter control schemes and their ability to compensate for lack of system inertia have been investigated during this research program. Electromechanical oscillations that occur due to interactions between generators can be affected by inverter frequency support capabilities. The impact of inverter control on these electromechanical oscillations have also been studied.