Research On Control Of Marine Electric Propulsion System In Different Ocean Conditions

The marine electric propulsion system has characteristics of good economy, operation performance and high safety, which consists of drive motors and propeller loads. The permanent magnet synchronous motor has advantages of high magnetic flux and good dynamic property. As a result, the permanent magnet synchronous motor is widely used as a propel motor in marine electric propulsion system. This paper takes electric propulsion ship as the research object, and surveys are carried out on control strategies of the marine electric propulsion under different ocean conditions. The operations of ships are complex and continuous, and this paper utilizes different control strategies under different ocean conditions in order to guarantee ships are operated smoothly.Firstly, we set up models of the marine electric propulsion system, and analyze propeller loads in the system, including interactions between ship paddles, open-water performances of paddles and advance velocity ratio and so forth. Then, the resistance in ships operations and ship propulsion efficiency is analyzed. Since ship motion is a dynamic process, we make motional models on propeller, permanent magnet synchronous motor, load respectively, preparing different control strategies for different ocean conditions.Secondly, we utilize rotate speed control strategy under normal ocean conditions. The permanent magnet synchronous motor uses the direct torque control method. The normal ocean condition refers to a quiet sea, say, propeller load whelm is under the sea and there is no wind between propeller paddles. The aim of this control method is to guarantee the whole output speed of propeller paddle is the same as the given speed. The direct torque control strategy omits complicated vectors conversions, and has simple control structures, higher dynamic reflections. Through the result of simulations, the speed control method has good usage.Thirdly, as for the abnormal ocean conditions, we utilize a method called anti-overwinding method, which is similar to ABS in vehicle systems. The abnormal ocean condition refers to bad wave performances on ocean surfaces. Wind is present between propel paddles, and torque losses produce at the meantime under the abnormal ocean conditions. Therefore, ships operations are unsteady. Aiming at reducing rotate speed and too much torque loss, the anti-overwinding method is used, consisting of torque load examination, calculation of losses and wind observations. Mathematical models are set up respectively, and the reality of this control strategy is checked.Finally, different control strategies are investigated under different ocean conditions. This paper uses switch conversions control strategy to guarantee ship change its operation between different ocean conditions. The conversion theory is analyzed, and models on conversions are set. The problems of different ocean conditions are solved. Through results of simulation, the robustness of the control method is better, and it has steady performance.