Dynamics and Control of Inverter-Based Resources in Modern Power Systems

Electric power systems are undergoing drastic transformations from large synchronous generation to inverter-based resources (IBRs). Solar photovoltaic panels, wind turbines, batteries and fuel cells, for example, all connect to power systems through power electronic inverters. IBRs possess vastly different physics than traditional synchronous generators and their dynamics highly depend on the enforced controller. Existing control strategies for IBRs tend to be categorized as either grid-following or grid-forming. This talk presents a novel inverter control scheme that is in essence a hybrid grid-forming/following controller and offers beneficial characteristics of both. The controller incorporates both a phase-locked loop (PLL) for voltage synchronization and power frequency droop for load sharing. The distinguishing feature of the controller is that it regulates active power by adjusting the phase angle across the filter inductance. I will also discuss some practical features of the PLL-based control such as black-start and low voltage ride-through. Various analyses are carried out to explore the small- and large-disturbance performance under a variety of system conditions. Improved robustness is achieved by incorporating both power-frequency droop and a PLL into the control strategy.