Research On Seamless Grid-connected Control Strategy Of Ship Shore Power

When the ship is near the port,the diesel generator will produce a lot of pollution,such as waste gas and noise.With the rapid development of China’s economy,the demand for port construction is also increasing,so it is urgent to build green and low-carbon ports.Shore power technology refers to the use of Marine diesel generators during the ship’s landing at the port.The use of shore power by ships in port is of great significance for energy conservation,emission reduction and construction of green ports,and can effectively solve the pollution problems caused by the use of diesel generators by ships in port during the period of port arrival.Seamless grid-connected control is one of the core technologies of shore power system,which can provide uninterrupted and stable power for ships in port.This paper has carried on the modeling to the ship shore electricity system,including the shore electricity supply system mathematics model and the ship power system mathematics model.This paper has carried on the analysis to the ship shore electricity seamless grid connection process,the grid connection condition and the control principle,and it has carried on the research to the seamless grid connection control strategy.The main work of this paper is as follows:(1)Analyze the basic composition of ship shore power system,the power supply mode and distribution form of existing shore power system.This paper establishs the mathematical model of shore power supply system,including the mathematical model of power rectifier and inverter core components;The mathematical model of Marine power system,including diesel engine and speed control system,synchronous generator and excitation control system,is established,and the simulation model of shore power system is built on this basis.(2)The process and control principle of seamless connection of ship shore electricity are analyzed,and the consistency conditions of phase sequence,frequency,voltage and phase angle to achieve seamless connection are analyzed in detail.The key methods of seamless grid connection,such as phase sequence detection and adjustment,grid connection condition detection and adjustment,phase Angle pre-synchronization,inverse power protection,etc.,were studied.The phase sequence was determined by using the counter and the hardware zero indicator,and the phase sequence was automatically adjusted by the controller.The detection and adjustment module of voltage amplitude difference and frequency difference is designed,and the correctness of the method is verified by simulation.The phase Angle pre-synchronization control module is designed,and the simulation results show that the method can realize the fast synchronization of the voltage phase between the shore side and the ship side.Finally,a method of inverse power protection by eliminating closing Angle is proposed.(3)Two kinds of seamless network connection control strategies are studied.The first control strategy is the hybrid control strategy of P-Q to V-F,that is,in the process of gridconnection,the controller of the inverter on the opposite shore adopts P-Q control,and after grid-connection,P-Q control is transferred to V-F control,so as to achieve the stable voltage output from the shore side to the ship load,and better control effect can be obtained through simulation verification.The second kind of control strategy is that the inverter of the shore is controlled by droop control.This control strategy is improved by optimizing the traditional droop controllers and joining the virtual inertia link,which makes the shore side inverter devices have marine electrical characteristics.The simulation results show that the improved control strategy can realize the smooth switching between diesel generator and shore power,and verify the effectiveness of the strategy.Finally,through comparative analysis,the two control strategies have their own advantages,and can meet the requirements of the seamless network connection control strategy.