Research On The Seamless Connection And Disconnection Between Ship Grid And Shore Power Supply

In recent years,with the rapid growth of world trade and the effective promotion of China's “One Belt,One Road” strategy,the world shipping industry,including China,has generally shown a prosperous development trend.At the same time,the environmental problems brought by ships at berth have become increasingly prominent,which has attracted the attention of various port countries around the world.In this context,shore power supply technology has emerged.This technology can not only make the pollutant discharge of ships at berth close to zero,but also bring considerable economic benefits to the port and ships.At present,shore power converter system can provide 50/60 Hz dual-frequency AC voltage with adjustable amplitude for the ship.Among them,the topology research and steady-state operation control for the low-voltage shore power converter are relatively mature.In contrast,the topology structure selection of high-voltage shore power supply is more abundant,and the control strategy is more complicated.The related system research has not yet obtained large-scale mature commercial practice and needs to be improved.In addition,in order to avoid the economic loss caused by power failure when the ship is docked,the smooth access and disconnection of shore power supply has always been a key issue for the academic community and the industry.In response to the above problems,this paper has carried out the following work:(1)Research on the low-voltage shore power supply system.The mathematical model of the traditional two-level voltage source rectifier(VSR)and voltage source inverter(VSI)in synchronous rotating dq coordinate system is established.The voltage and current double closed-loop control strategy is adopted in the dq coordinate system,and the PI controller is used to realize fast tracking and no static difference control,thereby realizing the unit power factor of the grid side and load side output voltage control.The main circuit parameters such as the grid side filter,the DC side capacitor,and the load side filter are designed in combination with the performance requirements of the system.The effectiveness of the topology and control strategy of the low-voltage shore power converter was verified by simulation and experiment.(2)Research on the high-voltage shore power converter system.The modular multilevel converter(MMC)is selected as the commutation topology,and the basic working principle of the MMC and its mathematical model in the three-phase stationary abc coordinate system are analyzed.The principle of nearest level modulation and phase-shifted carriers modulation is expounded,and the harmonic level is compared and analyzed.The phase-shifted carriers modulation method is selected due to its lower harmonic level when the number of submodules is small.Aiming at the phenomenon that the loop current existing on the DC side of the MMC and sub-module capacitor voltage fluctuation,the double-frequency loop suppression strategy and the sub-module capacitor voltage sorting algorithm are used respectively,which provides good external characteristics for the voltage-current double closed-loop control strategy.In the main circuit parameter design part,the bridge arm inductance and sub-module are designed.Simulation and experiments verify the effectiveness of the topology and control strategy of the MMC shore power supply system.(3)Research on smooth switching technology for seamless access and unloading of ship power grids.Based on the analysis of shore power,marine diesel generator and ship load,the basic principle of phase-locked loop based on synchronous rotating coordinate system is analyzed,and the transfer function of shore power output voltage phase is derived to realize phase synchronization between shore power and ship grid.Aiming at the the power failure experienced by ships when connected to shore power,the mathematical model of the parallel connection between the shore power and the ship diesel generator is analyzed,and the relationship between voltage and current is derived.A load transfer algorithm based on the phase voltage reference value is proposed.The transfer algorithm realizes continuous and smooth switching between the shore power and the ship auxiliary machine.The effectiveness of the control algorithm was verified by simulation and experiment.(4)Build a hardware-in-the-loop simulation platform with DSP TMS320F28069 M and PLECS RT BOX as the core,RT BOX is used to realize the hardware-in-the-loop simulation of the hardware system,and DSP is used to realize the real-time sampling and switch control signal generation of the semi-physical model.The simulation platform further verified the structure and control strategy proposed in this paper.