Research On The Application Of Superconducting Magnetic Energy Storage For Improving The Stability Of Ship Power System

Ship power system(SPS)can be seen as an autonomous microgrid.Due to the relatively small capacity of power generation and the rapid changes of loads with characteristics of uncertain occurrence time and magnitude,ship power SPSs are more likely to face power quality issues like frequency variations than large interconnected power systems.Adding an energy storage device to the SPS can help suppress frequency oscillations caused by frequent switching actions of high-power loads,and improve the anti-disturbance capability of the ship microgrid.Among all energy storage technologies,superconducting magnetic energy storage(SMES)has certain advantages of high power density and fast response ability in participating in the dynamic adjustment process of the ship power system.Based on the background above,the application of SMES in SPSs is studied in this thesis.This thesis starts with the modeling of a notional SPS including SMES.Based on the operating characteristics of SPSs when the load changes,the control strategies of SMES for power compensation are analyzed and verified.Furthermore,considering the deficiencies of the two existing control strategies,an adaptive segmented control strategy is proposed.Then,according to the requirements of the application in SPSs for SMES,the optimal design method of SMES magnets is proposed and fully discussed.Finally,Finally,two optimized magnets are evaluated for AC loss,respectively.The main work and results achieved in the thesis are described as follows:(1)Based on the principles of system modeling,power system stability,control theory and simulation technology,the mathematical models and control methods of each part in the SPS including the generator,the gas turbine and its governor,the exciter,the propulsion motor,and the propeller load are analyzed.The entire model is built in Matlab/Simulink.The dynamic characteristics of the SPS under the conditions of ship starting,sailing with variable speeds and loading pulse load are studied in the simulation platform.(2)Two control strategies and their parameter values on the dynamic compensation effect are analyzed and verified in the simulations.Results show that the power compensation strategy based on exponential function responds faster to power demand while the one based on virtual inertia is more adaptive for load change.According to this conclusion,a segmented control strategy combining the advantages of the two strategies is proposed.To solve the shortage of the segmented control strategy in determining the compensation power of the SMES,an adaptive optimization control strategy of SMES to suppress the frequency oscillation when the ship is sailing with variable speeds is proposed.The simulation results show that,based on the adaptive segmented control strategy,the SMES can adaptively output the compensation power according to the the load variation of the SPS.(3)According to the performance index of SMES for application in the SPS,the magnet design method for high-temperature superconducting(HTS)ring-shaped SMES is proposed.Taking the total length of HTS tape and the volume of the magnet as the optimization targets,respectively,the electromagnetic optimization design of the magnet with energy storage not less than 22 MJ at the working temperature of 20 K has been completed.Based on the optimization results,the preliminary design concept of the magnet is summarized: within a certain range,decreasing the inner diameter of the coil and increasing the number of coils can reduce the volume of the magnet to improve space utilization,while increasing the inner diameter of the coil and reducing the number of coils can help cut down the total length of HTS tape to reduce the manufacturing cost of the magnet.Furthermore,comprehensively considering the high price of HTS tape and the limitation of ship space,the magnet structure is optimized with the mutually restrictive optimization objectives,tape length and magnet volume.Pareto optimal scheme that can be regarded as references for magnet design is provided.(4)The current waveforms of the SMES when the propulsion motor is startup and power down are extracted.The ac loss of the magnets with the optimal design aiming at the minimum wire consumption and the one aiming at the minimum volume are evaluated,respectively.The results show that in the process of power exchange between the SMES and the SPS,the ac loss of the magnet designed with the goal of minimum wire consumption is smaller than that of the magnet designed with the goal of the minimum volume.This conclusion can provide a certain reference for the the parameter optimization of the magnet.