Grid Fragility, Blackouts, and Control Co-Design Solutions

Abstract

The grid is undergoing a large-scale transformation, including a significant reduction of synchronous generators, a high penetration of inverter-based resources and renewables, substantial demand growth, new extra-large loads, aging infrastructure and a concerning vulnerability to contingencies. Some of the recent massive blackouts in Spain/Portugal, Chile and Texas are exposing the fragility of the grid as we know it today. This paper introduces new solutions to stabilize the grid under undesired dynamic interactions and extreme contingencies, with the goal of avoiding cascading failures and blackouts. Using control co-design methodologies, the paper proposes three interdependent categories to improve the reliability and controllability of the grid. The first category, or Flexible inverter-based resources (IBRs), proposes inverter-based generators with inverters that can transition from grid-following mode (for energy production) to grid-forming mode (for grid stability), have some form of fast short-term energy storage, and contain advanced control solutions for grid controllability and IBRs' coordination. The second category, or Intelligent relays, proposes advanced relays that include under-frequency and under-voltage load-shedding capabilities for emergency operation, with smart sensors and algorithms for automatic contingency prediction, impedance estimation and stability assessment. The third category, “2.5 control” or Wide-area real-time control co-design, adds a layer between the conventional secondary and tertiary control systems. It co-designs the dynamics of the grid in real-time, allocating the previous inertia (“energy”), damping (“control authority”) and load-shedding capabilities across different regions of the grid, according to the dynamic variations and stability needs of each location. These concepts have been recently proposed as part of a new ARPA-E effort, called the GRADIENTS program, opening the door to advanced control co-design opportunities to build the grid of the future.