Modeling and simulation of all-electric propulsion system with three-closed loop control

Abstract

Marine electric propulsion system is a complex power chain of ship-engine-propeller composed by inverter, propulsion motor and propeller. Ship power system is an independent power grid, its propulsion motor and propeller are easily affected by complex and variable sea environment and working conditions, which can easily cause shafting vibration or even malfunction and then affecting the power supply system. Its modeling is difficult. Simulation time is long. Torque fluctuations are frequent and so on. To solve these problems, a set of mathematical model of marine electric propulsion system including inverter, permanent magnet synchronous motor (PMSM), propeller and hull is established firstly. Based on the two-closed loop control of field-oriented control (FOC), a third closed-loop control, that is torque closed loop, is added to relieve torque fluctuations and the PI parameters are discussed of the controller. The anti-jamming and dynamic-static performance of the system under sudden changes by additional constant load, random fluctuating load and changing reference speed are analyzed. The experimental results show that the model can simulate the all-electric propulsion system very well. Three-closed loop control reduces the vibration of the motor shaft and makes the propulsion system to follow the reference speed quickly and keep the torque stable than the two-closed loop control when the propeller torque and the reference speed is changing.