ADRC‐SMC‐based disturbance rejection depth‐tracking control of underactuated AUV

Abstract The underactuated autonomous underwater vehicle (AUV) depth‐tracking approach is presented in this research along with comparative field experiments. First, a model‐free ADRC‐SMC pitch autopilot method is proposed to eliminate dynamics‐related disturbances. The active disturbance rejection control (ADRC) framework is adopted to compensate the complicated and unknown pitch dynamics into an approximate integral series type. Sliding mode control (SMC) feedback law is designed to further compensate for dynamic feedback linearization inaccuracy of the ADRC framework. Second, the disturbance rejection double‐loop depth‐tracking approach is suggested in conjunction with adaptive line‐of‐sight (ALOS), which converts depth tracking into pitch tracking. The ALOS not only estimates the actual angle of attack but also compensates the pitch‐tracking inaccuracy from the ADRC‐SMC in the inner loop. Then, the uniformly semiglobally exponential stability of the closed‐loop depth controller is proved after a detailed analysis of the stability from the inner loop to the outer loop. Finally, comparative field experiments are conducted to verify the proposed method. The effectiveness and strong disturbance rejection capabilities of the ADRC‐SMC pitch autopilot method and the suggested depth‐tracking approach are demonstrated by experimental results.