Transient and disturbed propeller load compensation in hybrid propulsion using propeller estimator and predictive control

We address the design of a predictive power-split management system for the transient and fluctuating propeller load sharing. Modeling of the power system was carried out based on experimental data gathered from the hybrid plant and on first principles for the diesel engine behavior and battery charging. Propulsion plant and wave disturbance models are employed to simulate realistic marine load application that affects the powerplant operation. A propeller observer is developed to provide the propeller law parameter to the controller, in order to perform load estimation and prediction based on shaft speed elevation. A Nonlinear Model Predictive Controller (NMPC) is designed for the optimal transient power-split problem of a hybrid diesel-electric marine propulsion plant. The NMPC scheme directly controls the torque output of the diesel engine and the electric motor generator ensuring that certain constraints concerning the system overloading are met, avoiding fast accelerations, and load fluctuations of the diesel engine that affect engine performance. The control system was experimentally tested in real-time operation in a physical testbed. Results showed that controller rejected successfully load disturbances and maintained the desired rotational speed of the powertrain as well as the desirable state of charge in battery within the power plant limits, achieving smooth power transitions and compensation of power fluctuations of the diesel engine.