A four quadrant finite dimensional thruster model

This paper reports two specific improvements in the finite-dimensional nonlinear dynamical modeling of marine thrusters using direct drive brushless DC motors with a PWM converter. Previously reported four-quadrant models have employed airfoil theory considering only axial fluid flow and using sinusoidal lift/drag curves. First, we present a thruster model incorporating the effects of rotational fluid velocity and inertia on thruster response. Second, we report a novel method for experimentally determining nonsinusoidal lift/drag curves. The model parameters are identified using experimental thruster data (force, torque, fluid velocity). The models are evaluated by comparing experimental performance data with numerical model simulations. The data indicates that thruster models incorporating both reported enhancements provide superior accuracy in both transient and steady-state response.