An Online Data-Driven Method for Microgrid Secondary Voltage and Frequency Control With Ensemble Koopman Modeling

• Published in: IEEE transactions on smart grid Vol. 14; no. 1; pp. 68 - 81
• Main Authors: Gong, Xun, Wang, Xiaozhe, Joos, Geza
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.01.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptation models; Adaptive control; Adaptive Koopman operator optimal control; Asymptotic stability; Basis functions; data-driven control; Distributed generation; Effectiveness; Electric potential; Frequency control; Iterative methods; Koopman-based ensemble learning; Load modeling; measurement-based estimation; microgrid secondary control; Model accuracy; Modelling; Noise measurement; Nonlinearity; Optimal control; PMU; Power system stability; Stability criteria; State space models; Topology; Voltage; Voltage control
• ISSN: 1949-3053; 1949-3061
• DOI: 10.1109/TSG.2022.3190237

Low inertia, nonlinearity and a high level of uncertainty (varying topologies and operating conditions) pose challenges to microgrid (MG) systemwide operation. This paper proposes an online adaptive Koopman operator optimal control (AKOOC) method for MG secondary voltage and frequency control. Unlike typical data-driven methods that are data-hungry and lack guaranteed stability, the proposed AKOOC requires no warm-up training yet with guaranteed bounded-input-bounded-output (BIBO) stability and even asymptotical stability under some mild conditions. The proposed AKOOC is developed based on an ensemble Koopman state space modeling with full basis functions that combines both linear and nonlinear bases without the need of event detection or switching. An iterative learning method is also developed to exploit model parameters, ensuring the effectiveness and the adaptiveness of the designed control. Simulation studies in the 4-bus (with detailed inner-loop control) MG system and the 34-bus MG system showed improved modeling accuracy and control, verifying the effectiveness of the proposed method subject to various changes of operating conditions even with time delay, measurement noise, and missing measurements.