Comparative Study of Heading and Speed Control Techniques for Small Autonomous Surface Vehicles

Due to varying and unpredictable sea/ocean environments, Autonomous Surface Vehicles (ASVs) require robust and reliable speed and heading control to autonomously navigate and successfully complete given mission tasks. In the paper, the authors consider the speed and heading control of an ASV whose decision processes (given specific mission goals) are solely determined by on-board autonomy software platform, Mission Oriented Operating Suite-Interval Programming (MOOS-IvP). Here, the “front seat” control of the ASV is only privy to speed and heading commands and not the nature of the desired ASV trajectories. The test vehicle in this study is an autonomous Rigid Hull Inflatable boat (RHIB), whose model dynamics are not perfectly known. The purpose of this research is to determine and identify model-based control techniques that can be easily implemented, tuned, and provide reliable speed and heading control under this autonomy architecture. Control techniques studied in this paper include PID control, PID-based Sliding Mode Control (SMC-PID), and Adaptive Linear Quadratic Regulators (ALQR). Rudder saturation control to prevent additional steering phase lag is also investigated. All control techniques are numerically simulated and implemented using the MOOS-IvP autonomy control platform on board the Seafox, a Rigid Hull Inflatable boat (RHIB) platform. The control techniques are implemented in Seafox and tested on the Puget Sound on the Naval Undersea Warfare Center (NUWC) Division, Keyport Range Complex. Analysis of numerical simulations show that SMC and ALQR have higher performance in both speed and heading control, and rudder rate saturation is very effective in preventing over steering. However, field tests with the Seafox show that speed and heading control with PID control is sufficient and, often times, better than that with the SMC and ALQR. No conclusions, yet, can be drawn regarding the efficacy of rudder rate saturation.