Empowering the Grid: Decentralized Autonomous Control for Effective Utilization and Resilience

Abstract

With the emergence of low-inertia microgrids powered by inverter-based generation, there remains a concern about the operational resilience of these systems. Grid-forming inverters (GFMs), enabled by various device-level (primary) and system-level (secondary) control methods, are poised to play a significant role in achieving certain operational objectives, such as the effective utilization of clean energy resources while maintaining stability. However, despite the recent advances in GFMs, there is a lack of suitable controls that can ascertain resilience-constrained operations, like maintaining critical operational safety limits during transients under various cyber-physical disruptions. In this work, we develop decentralized autonomous controllers (DACs) that enforce resilience-constrained operation via local, minimally invasive adjustments (e.g., changes in set-points) while co-existing within the hierarchy of existing (primary and secondary) controls. The DACs work autonomously by sensing only local GFM measurements and act only when operational resilience constraints are violated. The proposed DAC scheme is computationally efficient (only algebraic computations), which enables fast, real-time execution and demonstrates the efficacy of the proposed control framework on GridLAB-D-HELICS-based control-grid co-simulations on the IEEE 123-node networked microgrid. Finally, we show how the developed DACs empower the grid by utilizing the available resources entirely to ensure resilience (maintain frequency safe limits).

Figures (11)

• Figure 1: CERTS droop-controlled GFM inverter model, with (a) Q-V droop control, and (b) P-f droop control, including over- and under-load mitigation (adopted from du2020modeling).
• Figure 2: Overview of the functioning of the proposed DAC: These inverter-based controls are located between primary and secondary controls. When the frequency resilience constraints are violated, these controls adjust the secondary control set-points to ensure frequency resilience, otherwise, these controls will not intervene and pass the secondary control set-points to the inverter. These autonomous controls are computationally efficient and rely solely on local measurements available at the inverters themselves.
• Figure 3: DAC implementation at each inverter. $P_\textrm{set}^*$ denotes the set-point sent by the secondary control, $\mu = (S_{\textrm{inv}}, m_p)$ denotes the fixed parameters at the inverters and $x = (\omega, P_{\textrm{inv}}, Q_{\textrm{inv}})$ denote the measurements from the inverter.
• Figure 4: Illustration of the functioning of safety promoting DACs when frequency violations occur.
• Figure 5: Control-grid co-simulation framework used for the simulation study.