Design of an adaptive PI speed controller for FOC-driven underwater thrusters

Abstract

Underwater thrusters are the primary actuators in marine vehicles. The thruster drive and control methods for these thrusters considerably influence their dynamic response, accuracy, and efficiency. This study reviewed the structure of field-oriented control (FOC) and six-step commutation (SSC)—driven thrusters, comparing their advantages and disadvantages in underwater applications. Considering the dynamic performance of open-loop SSC, the precision of closed-loop SSC, and the energy efficiency of FOC, an adaptive proportional–integral (API) speed controller was introduced for FOC-driven underwater thrusters, which demonstrated superior performance in underwater conditions. Simulations were conducted to reveal the performance differences between FOC- and SSC-driven underwater thrusters and the advantages of the designed API controller in FOC-driven systems. FOC with a conventional PI speed controller exhibited a chattering-free steady state and 22.9% higher energy efficiency than the closed-loop SSC, and the API-based FOC showed improved step signal response and a 25.9% increase in amplitude bandwidth compared with conventional PI and integral-separated PI control. Furthermore, the API controller avoided speed chattering at low speed and displayed lower steady-state error than the conventional PI controller. These results support the conclusions of the higher bandwidth and overshoot avoidance of API and the higher energy efficiency of the FOC-driven motor.