To meet the development requirements of the path planning unit for unmanned underwater vehicles (UUVs), research is conducted on UUV 3D obstacle avoidance path planning algorithms and software design. Firstly, aiming at the problem of underwater 3D obstacle avoidance path planning for UUVs, a global path planning algorithm based on the improved D* Lite is designed, and a local path planning algorithm combining the 3D obstacle avoidance strategy and the improved artificial potential field (APF) algorithm is designed. Secondly, based on the above path planning algorithms, a UUV 3D obstacle avoidance path planning software is developed under the Robot Operating System 2 (ROS2) framework and deployed on an Orange Pi 5B. To test the algorithms and the developed software, a UUV autonomous navigation hardware-in-the-loop (HIL) simulation system is constructed. Finally, based on this system, three types of HIL simulation experiments are conducted, including global path planning, local path planning, and comprehensive obstacle avoidance path planning. The simulation experiments show that the improved D* Lite-APF algorithm has better comprehensive performance than the traditional D* Lite-APF algorithm; the path planning software can guide the UUV to reach the goal point safely and runs stably and reliably. The designed UUV 3D obstacle avoidance path planning algorithm and software exhibit good obstacle avoidance performance and can be applied to the rapid development of actual UUV path planning units.

To fulfill the requirements for rapid development of high-performance AUV motion control systems, a three-dimensional (3D) path- following control system is designed and implemented based on the MOOS-IvP/ArduSub architecture. Using Lyapunov stability theory, an adaptive line-of-sight (ALOS) guidance law with variable look-ahead distances (V$\Delta$-ALOS) is designed. Furthermore, based on pole placement, kinematic controllers for yaw angle and depth, along with dynamic controllers for surge velocity, yaw rate, and pitch angle, are designed, enabling dual-mode control comprising decoupled steering/diving plane control and 3D spatial path- following control. On the established simulation platform, hardware-in-the-loop (HIL) comparative experiments are conducted for two typical 3D paths (a “straight line–turning circle–straight line” path and a sinusoidal path) under compound disturbances including ocean currents, parametric uncertainty, communication delays, and sensor errors. The experimental results demonstrate that the proposed V$\Delta$-ALOS guidance law exhibits significant advantages over the integral line-of-sight (ILOS) guidance law and two existing ALOS guidance laws in terms of dynamic performance and steady-state accuracy, with slightly lower propulsion control effort.