Hierarchical inner outer LQR-PID controller based on high-order sliding mode observer for underwater remotely operated vehicle

Abstract

This paper presents a hierarchical inner–outer linear quadratic regulator-proportional integral derivative (LQR–PID) control architecture integrated with a high-order sliding mode (HOSM) observer for precise motion control of an underwater remotely operated vehicle (ROV) operating in uncertain and highly nonlinear environments. The proposed control strategy is structured into two coordinated layers: An inner-loop LQR controller for dynamic stabilization and disturbance attenuation, and an outer-loop PID controller for trajectory tracking and set-point regulation. The control system has been organized into a two-layer structure: The inner loop based on an LQR controller to manage fast dynamics and compensate for unmodelled underwater effects. The outer loop utilizes a PID controller to guaranty smooth tracking performance and maintain robustness against parameter variations. To deal with limited sensors, a HOSM observer is applied to estimate the states that cannot be measured and to handle uncertainties. By combining the PID–LQR controller with the HOSM observer, the system becomes more robust, faster in response, and more accurate than using either LQR–HOSM or PID control alone. Simulations with a comparative study between these scenarios show better tracking for PID_LQR_HOSM overall system under varying ocean currents, and tests on a 1-meter ROV confirm its effectiveness for advanced navigation and manipulation tasks.