Proximate time optimal for the heading control of underactuated autonomous underwater vehicle with input nonlinearities

In this paper, a modified proximate time-optimal control (PTOC) is proposed based on reduced order extended state observer (RESO) and controller scaling method, for the heading control of underactuated autonomous underwater vehicles (AUV) with input nonlinearities. First, a simple and practical modified ADRC is proposed for heading control with input nonlinearities. The non-symmetric dead-zone with unknown parameters is modeled as a combination of linear input and bounded disturbances, and the RESO is designed to estimate and compensate it. The influence of actuator saturation constraint is reduced by limiting the control signal before it goes into the RESO. Then, a parameter self-tuning strategy is proposed for the feedback controller with the changed control gain by the controller scaling method. The control gain is quadratic respect to the velocity of AUV, the active disturbance rejection control (ADRC) controller parameters can be adjusted based on the AUV velocity using the strategy. And finally, the modified PTOC, based on RESO and with an updating strategy for the limit of linear region, is proposed to improve the control performance. Several simulation experiments are carried out, the effectiveness of self-tuning modified ADRC is verified, and the proposed modified PTOC shows better performance.