Robust Position Control of VTOL UAVs Using a Linear Quadratic Rate-Varying Integral Tracker: Design and Validation

Saleem, Omer; Kazim, Muhammad; Iqbal, Jamshed

Abstract

This article presents an optimal tracking controller retrofitted with a nonlinear adaptive integral compensator, specifically designed to ensure robust and accurate positioning of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) that utilize contra-rotating motorized propellers for differential thrust generation. The baseline position controller is synthesized by employing a fixed-gain Linear Quadratic Integral (LQI) tracking controller that stabilizes position by tracking both state variations and pitch-axis tracking error integral, which adjusts the voltage to control each coaxial propeller’s speed accurately. Additionally, the baseline tracking control law is supplemented with a rate-varying integral compensator. It operates as a nonlinear scaling function of the tracking-error velocity and the braking acceleration to enhance the accuracy of reference tracking without sacrificing its robustness against exogenous disruptions. The controller’s performance is analyzed by performing experiments on a tailored hardware-in-the-loop aero-pendulum testbed, which is representative of VTOL UAV dynamics. Experimental results demonstrate significant improvements over the nominal LQI tracking controller, achieving 17.9%, 61.6%, 83.4%, 43.7%, 35.8%, and 6.8% enhancement in root mean squared error, settling time, overshoot during start-up, overshoot under impulsive disturbance, disturbance recovery time, and control energy expenditure, respectively, underscoring the controller’s effectiveness for potential UAV and drone applications under exogenous disturbances.

Citation

Saleem, O., Kazim, M., & Iqbal, J. (2025). Robust Position Control of VTOL UAVs Using a Linear Quadratic Rate-Varying Integral Tracker: Design and Validation. Drones, 9(1), Article 73. https://doi.org/10.3390/drones9010073

• Journal Article Type: Article
• Acceptance Date: Jan 16, 2025
• Online Publication Date: Jan 19, 2025
• Publication Date: Jan 1, 2025
• Deposit Date: Jan 16, 2025
• Publicly Available Date: Jan 20, 2025
• Journal: Drones
• Electronic ISSN: 2504-446X
• Publisher: MDPI
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 1
• Article Number: 73
• DOI: https://doi.org/10.3390/drones9010073
• Keywords: VTOL UAVs; Position tracking; Linear quadratic integral control; Rate-varying integral compensator; Hyperbolic function; Hardware-in-the-loop validation
• Public URL: https://hull-repository.worktribe.com/output/5004913
• Publisher URL: https://www.mdpi.com/2504-446X/9/1/73