@article{siddiqui_deese_vermillion_2023, title={Recursive Gaussian Process-Based Adaptive Control of a Ducted Kite System for Tidal Energy Harvesting}, volume={31}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2023.3243441}, abstractNote={In this brief, we introduce an adaptive control approach for a novel tidal energy harvesting device called the Duct-Sail. The design combines features of kite-based energy-harvesting devices and ducted turbines to realize power augmentation through cross-current flight at low flow speeds along with the flow augmentation, stationary performance potential, and protection offered by a duct. At low flow speeds, the Duct-Sail executes high-speed figure-8 cross-current flight to generate rated power. At higher flow speeds, it curtails its cross-current motion to limit structural loading while still delivering rated power. We present a detailed dynamic model of the system along with design parameters for an initial prototype. We also present model-based and nonmodel-based adaptive control strategies that are used to control the intensity of cross-current flight in a time-varying flow profile. Lastly, we present simulation results using the real flow data from a candidate installation site, which enables a practically meaningful comparison of various adaptive control strategies.}, number={4}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Siddiqui, Ayaz and Deese, Joe and Vermillion, Chris}, year={2023}, month={Jul}, pages={1949–1956} }
 @article{siddiqui_borek_vermillion_2022, title={A Fused Gaussian Process Modeling and Model Predictive Control Framework for Real-Time Path Adaptation of an Airborne Wind Energy System}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2022.3178038}, abstractNote={This article presents a computationally tractable adaptive control strategy suitable for mobile systems operating in a stochastically and spatiotemporally varying environment by fusing Gaussian process modeling and receding horizon control. This strategy ideally manages the tradeoff between exploration (maintaining an accurate estimate of the stochastic resource) and exploitation (maximizing a performance index, which generally consists of harvesting the resource) subject to partial observability (stochastic resource only measurable at the system’s location) and mobility constraints, which are characteristic of dynamic systems. The case study in this article focuses on a crosswind airborne wind energy (AWE) system where the wind turbine tower is replaced by tethers and a lifting body, allowing the system to adjust its altitude, with the goal of operating at the altitude that maximizes net energy production in a wind environment that is changing in altitude and time. Real wind speed versus altitude data has been used to validate the strategy and results are presented for a variety of control strategies applied to a rigid wing-based AWE system.}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Siddiqui, Ayaz and Borek, John and Vermillion, Chris}, year={2022}, month={Jun} }
 @article{cobb_reed_daniels_siddiqui_wu_fathy_barton_vermillion_2021, title={Iterative Learning-Based Path Optimization With Application to Marine Hydrokinetic Energy Systems}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2021.3070526}, abstractNote={This article presents an iterative learning control (ILC)-based approach for optimizing the flight path geometry of a tethered marine hydrokinetic (MHK) energy system. This type of system, which replaces the tower of a conventional system with a tether and a lifting body, can capture energy either through an on-board rotor or by driving a generator with tension in the tether. In the latter mode of operation, which represents the focal point of this effort, net positive energy is generated over one cycle of high-tension spool-out followed by low-tension spool-in. Because the net energy generation is sensitive to the shape of the flown path, we employ an iterative learning update law to adapt the path shape from one lap to the next. This update law is complemented with an iterative power take-off (PTO) controller, which adjusts the spooling profile at each iteration to ensure zero net spooling. We present and validate the proposed control approach in both uniform and spatiotemporally varying turbulent flow environments, based on a realistic ocean model detailed in this article. Finally, based on simulation results across a wide range of excitation levels, we perform a simulation-based assessment of convergence properties, comparing these results against bounds derived in the authors’ prior work.}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Cobb, Mitchell and Reed, James and Daniels, Joshua and Siddiqui, Ayaz and Wu, Max and Fathy, Hosam and Barton, Kira and Vermillion, Chris}, year={2021}, month={Apr} }
 @article{reed_cobb_daniels_siddiqui_muglia_vermillion_2020, title={Hierarchical Control Design and Performance Assessment of an Ocean Kite in a Turbulent Flow Environment}, volume={53}, ISSN={["2405-8963"]}, DOI={10.1016/j.ifacol.2020.12.1887}, abstractNote={This paper presents a hierarchical control framework for a kite-based marine hydrokinetic (MHK) system that executes power-augmenting cross-current flight, along with simulation results based on a high-fidelity turbulent flow model that is representative of flow conditions in the Gulf Stream. The hierarchical controller is used to robustly regulate both the kite's flight path and the intra-cycle spooling behavior, which is ultimately used to realize net positive energy production at a base station motor/generator system. Two configurations are examined in this paper: one in which the kite is suspended from a surface-mounted platform, and another in which the kite is deployed from the seabed. To evaluate the robustness of this control framework in a realistic ocean environment, we present simulation results whereby we superimpose low-frequency data from the Mid Atlantic Bight South Atlantic Bight Regional Ocean Modeling System and acoustic Doppler current profiler measurements with a high-frequency turbulence model, resulting in a high-fidelity 3D spatiotemporal flow field that is presented to the kite system. Based on this simulation framework, we demonstrate the effectiveness of the control system both in terms of robust flight and power generation.}, number={2}, journal={IFAC PAPERSONLINE}, author={Reed, James and Cobb, Mitchell and Daniels, Joshua and Siddiqui, Ayaz and Muglia, Michael and Vermillion, Chris}, year={2020}, pages={12726–12732} }
 @article{siddiqui_naik_cobb_granlund_vermillion_2020, title={Lab-Scale, Closed-Loop Experimental Characterization, Model Refinement, and Validation of a Hydrokinetic Energy-Harvesting Ocean Kite}, volume={142}, ISSN={["1528-9028"]}, DOI={10.1115/1.4047825}, abstractNote={Abstract
               This paper presents a study wherein we experimentally characterize the dynamics and control system of a lab-scale ocean kite, and then refine, validate, and extrapolate this model for use in a full-scale system. Ocean kite systems, which harvest tidal and ocean current resources through high-efficiency cross-current motion, enable energy extraction with an order of magnitude less material (and cost) than stationary systems with the same rated power output. However, an ocean kite represents a nascent technology that is characterized by relatively complex dynamics and requires sophisticated control algorithms. In order to characterize the dynamics and control of ocean kite systems rapidly, at a relatively low cost, the authors have developed a lab-scale, closed-loop prototyping environment for characterizing tethered systems, whereby 3D printed systems are tethered and flown in a water channel environment. While this system has been shown to be capable of yielding similar dynamic characteristics to some full-scale systems, there are also fundamental limitations to the geometric scales and flow speeds within the water channel environment, making many other real-world scenarios impossible to replicate from the standpoint of dynamic similarity. To address these scenarios, we show how the lab-scale framework is used to refine and validate a scalable dynamic model of a tethered system, which can then be extrapolated to full-scale operation. In this work, we present an extensive case study of this model refinement, validation, and extrapolation on an ocean kite system intended for operation in the Gulf Stream or similar current environments.}, number={11}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Siddiqui, Ayaz and Naik, Kartik and Cobb, Mitchell and Granlund, Kenneth and Vermillion, Chris}, year={2020}, month={Nov} }
 @article{daniels_reed_cobb_siddiqui_vermillion_2020, title={Optimal Cyclic Spooling Control for Kite-Based Energy Systems}, volume={53}, ISSN={["2405-8963"]}, DOI={10.1016/j.ifacol.2020.12.1883}, abstractNote={This paper presents a control strategy for optimizing the the spooling speeds of tethered energy harvesting systems that generate energy through cyclic spooling motions which consist of high-tension spool-out and low-tension spool-in. Specifically, we fuse continuous-time optimal control tools, including Pontryagin’s Maximum Principle, with an iteration domain co-state correction, to develop an optimal spooling controller for energy extraction. In this work, we focus our simulation results specifically on an ocean kite system where the goal is to optimize the spooling profile while remaining at a consistent operating depth and corresponding average tether length. This paper demonstrates a 14-45% improvement (depending on the operating tether length and environmental flow speed) in power generation compared to a baseline, heuristic, control strategy.}, number={2}, journal={IFAC PAPERSONLINE}, author={Daniels, Joshua and Reed, James and Cobb, Mitchell and Siddiqui, Ayaz and Vermillion, Chris}, year={2020}, pages={12719–12725} }