Research On Grid Connection Control And Transient Stability Of Ship Shaft With Brushless Doubly-Fed Generator

Compared with the traditional AC brush motor,the brushless doubly-fed generator eliminates the brush and sliding ring devices,and improves the working safety and reliability.The unique advantages of variable speed and constant frequency of the motor make it have broad application prospects in the marine shaft power generation system.However,due to the complex internal structure,parameters and control strategy of the generator,the stability of the output voltage of the generator is often poor when it is connected to the marine power grid.It is difficult to meet the grid-connected conditions of the shaft generator,which will have a greater impact on the power grid,thereby affecting the stability of the marine power grid.Therefore,this thesis took the ship shaft brushless doubly-fed generator as the research object.Aimed at the control of the motor when connected to the ship grid and the transient stability of the system when connected to the grid,the control method of the generator output voltage amplitude,frequency and phase is proposed.The simulation model was built in the Simulink simulation platform,and the feasibility of the control method was verified by experiments.Firstly,the basic principle and different operation modes of brushless doubly-fed machine were introduced,and the power flow relationship of the machine at sub-synchronous speed was analyzed.The mathematical model of the motor in three-phase static coordinate system and two-phase rotating d-q coordinate system was deduced.On this basis,the mathematical model of brushless doubly-fed machine based on rotor speed coordinate system was further deduced.At the same time,the mathematical model of excitation and speed regulation system of marine synchronous generator was deduced.Secondly,the axle-band brushless doubly-fed generator connected to the grid required the phase-locked loop(PLL)to detect the voltage information of the ship power grid.Aimed at the problem that the response speed and detection accuracy of the traditional PLL can not meet the requirements of the ship power grid,a phase-locked loop based on double generalized second-order integrator was designed.The simulation results showed that the PLL can accurately detect the frequency and phase of the ship power grid voltage.The accurate information of grid voltage was provided for the following phase tracking and grid-connected control of brushless doubly-fed generator.Then,analyzed the structure of the grid-connected system of the ship shaft brushless doubly-fed generator.Accorded to the requirements of grid-connected of the shaft generator and the ship grid,scalar control and stator flux vector control were proposed for the amplitude-frequency control.At the same time,the designed phase-locked loop was used to detect the grid voltage and track the phase of the output voltage of the generator to meet the grid-connected requirements of the shaft generator.The simulation experimented under different conditions verify the stability and feasibility of the control methodFinally,on the basis of describing the transient stability characteristics of marine power system,analyzed the transient response process and transient response characteristics of grid-connected brushless doubly-fed machine.The influence of transient power angle and transient voltage stability on the transient stability of the system was studied in depth,and its influencing factors and influencing mechanism were determined.An energy function method was proposed to analyze the effect of sudden load change on the transient stability of power system.