Research On Control Strategy For Frequency Converter Of Marine Electric Propulsion System

In order to protect our vast territorial waters,we need to be a maritime power. Electric propulsion has many significant features such as energy saving, compact in size and cost-effective comparing with traditional power. The developed countries have already taken focus on the marine electric propulsion. In this paper, a systematic study on frequency converter control based on DC zonal electric distribution system is proposed to improve the stability margin of marine electric propulsion system.First of all, this paper introduces the development status and the main research directions of the marine electric propulsion system. A relatively intact mathematical model of marine electric propulsion system including three phase AC power, non-controlled rectifier,LC filter,inverter,propulsion motor and propeller is built. The typical operating conditions of the ship and the interaction effect between ship pitching motion heave and propulsion systems are also taken into account.Secondly, the influence of stability with rapid change in load of electric propulsion system is analyzed. Ship electric propulsion system will be simplified as a cascade system equivalent source subsystem and load subsystem and several stability criterions for cascade system are compared. The output impedance of the source subsystem constituted by three phase AC power, non-controlled rectifier and LC filter is derived. The input impedance of the load subsystem constituted by inverter, propulsion motor and propeller is also derived. A stability criterion named passivity-based stability criterion (PBSC) with more simple and effective characteristics for interconnected system is proposed.Finally, several frequency converter control strategies of marine electric propulsion system are analyzed. The impact with electrical, control and operating parameters on stability of DC zonal electric distribution system is studied. The compensation mechanism to enhance the stability of the DC bus voltage is analyzed. Then, a converter control strategy based on current disturbance observer (CDOB) which can improve the passive of the interconnected system by changing the input impedance of load subsystem is proposed.Thus, the stability of marine electric propulsion is greatly improved. The result of simulation based on MATLAB of marine electric propulsion system verifies the validity of the research.