Modeling And Research On The Stability Of Marine Electric Propulsion System

Ship electric propulsion system is the trend of the future development of propulsion motor directly from the power grid to take the way to replace the diesel engine shaft with the propulsion motor way.Propulsion system has the characteristics of high power and randomness.Frequent start-stop change will cause impact on the power grid,and cause the fluctuation of the power grid.The fluctuation of the power grid will also affect the normal operation of the propulsion system and the stabilization of other electrical equipment.Based on the above problems,the stability of the ship electric propulsion system is studied.The paper mainly includes the following aspects.First,The key modules(diesel prime mover,synchronous generator,propulsion motor and propeller load)in the ship electric propulsion system are modeled and the simulation of the rated working condition is carried out under the background of a subject research.It is proved that the model is reasonable.Second,The traditional controllable phase compound excitation controller is difficult to achieve the desired control effect because of the load variation.In this paper,two kinds of exciting systems,controllable phase compound excitation controller + power system stabilizer(PSS)and DC bus control are designed.The controllable phase compound excitation + PSS can compensate the negative damping in the system and suppress the voltage fluctuation in the system,but can not directly control the DC bus voltage stability.The excitation system based on DC bus control can directly control the DC bus voltage stability,System DC power distribution needs,than the control phase compound excitation + PSS control more adaptable to future development needs.Third,Based on the problem of voltage fluctuation of propulsion motor in propulsion system of ship electric propulsion system,two control methods of slip frequency scalar control and vector control based on magnetic field orientation are introduced,and the simulation under nominal condition is carried out.The results show that based on magnetic field Directional vector control is superior to the slip frequency control in the index such as speed overshoot,torque ripple and bus voltage drop in propulsion motor starting,and is more suitable for ship electric propulsion system studied in this paper.Fourth,Aiming at the problem of frequency fluctuation of the power system when the pulsed load is working,a multi-agent control system is designed in this paper.The system includes the propulsion motor agent,the pulse load agent,the system loss agent and the daily load agent.The fuzzy PID controller is used in the propulsion motor agent.The system can coordinate the power of the load in the grid and control it in real time Pulse load operating time.The simulation results show that the propulsive motor can fully compensate the pulse load power and the pulsed load overcurrent condition.Simulation results show that multi-agent control method can solve the fluctuation of grid frequency under the condition of pulsed load operation,cut off the electricity load in the power system,and protect the cable under over current effectively.