Research On Simulation Technique On Shipboard Integrated Electric Propulsion System

Shipboard integrated electric propulsion systems(IEPS)represent the future trend of ships.At this stage,it is necessary to take full advantages of the system and overcome its shortcomings through the design and development due to the complexity of the system.Traditional design from experience with low efficiency and high cost characteristics,and repeated tests to find solutions from the failure is not practical for complex systems.Even more,experimental tests are not feasible in some extreme conditions.Therefore,application of predictive modeling and simulation techniques in design and development for the system can provide useful help for better understanding of the dynamics of the system and parameter design.In this thesis,the problems in the modeling and simulation for shipboard integrated electric propulsion systems are researched.Firstly,the components and structure of the IEPS with Medium Voltage DC(MVDC)distribution are proposed for the research in this thesis.Modeling of the main equipments are implemented.As for the key components in IEPS such as generators and propulsion motors,the research on the modeling approach is carried out.The VBR model is incorporated in the modeling of the six-phase synchronous generators against for the shortcomings of the traditional d-q models.Aiming at the problems in flux saturation modeling,an approach using single saturation factor combining with function fitting is proposed,and the cross saturation in d-q axis is modelled.In order to transform the couplings between the two stator windings into the stator branches,the Park's inverse transformation is employed.Then the VBR model for the six-phase synchronous generator is constructed and validated.Furthermore,a technique using ideal transformer model to simulate the space vector decomposion is proposed to account for the reference frame transformation in the modeling of the multiphase induction motors.The asymmetrical six-phase induction motor is taken as an example,by which the simiulation test is implemented and the model is validated.Secondly,a numerical simulation testbed for shipboard MVDC IEPS is constructed.The model library for shipboard IEPS is constructed in Simulink.As for the simulation programs,the characteristic of the shipboard MVDC IEPS is analyzed.The simulation of the generation system,propulsion system and whole system with variaous operating conditions is carried out.Aiming at the problem that the system relates to multi-physical domains such as electricity,magnetism and mechanism and the inherent stiff,the software environment which employs Simulink combing PLECS is proposed in order to take full advantages of the two softwares.A constant switching frequency dirct torque control scheme for the induction motor is employed to avoid the disadvantages of traditional torque control schemes including disability to operate with four-quadrant drive,cannot employ average value model and poor control performance.In order to realize multi-operating conditions,the combination procedure of the four quandrant propeller model with the dirct torque control system is given.The simulation for various operating conditions in normal and emergency conditions is realized.At last,the simulation testbed is constructed based on the model library and simulation programs.Thirdly,due to the fact that there are voltage instability problems in the system,the eigenvalue analysis based on the small signal model is employed to analyze the stability of the system.A generator VBR model combining with diode rectifier AVM method is proposed in the generation system.The algabric loops is broken by employing low pass filters in the current branches.The 14-order nonlinear ODE is achieved for the generation system feeding constant power loads in MVDC IEPS.In the propulsion system,the induction motor model in stator flux reference frame combining the average model of PWM-VSI method is proposed to construct the ODE model.By replacing the ideal constant power load,the 23-order ODE model for the MVDC IEPS is obtained.Detailed simulation shows that the added low pass filters cannot affect the accuracy of the system and the non-linear ODE model is credible.The stability analysis for the generation system and the whole system is implemented through the analysis of the eigenvalue loci based on the small signal model.The results of the analysis are validated by detailed simulation of the simlation testbed.Finally,for the problem that there are many uncertain factors faced in the operation of shipboard IEPS,a method to construct multi-dimensional generalized Polynomial Chaos(gPC)through tensor product is proposed to carry out the uncertainty simulation.The proposed multi-dimensional gPC is first applied in a first order stochastic differential eqution.The procedure for the uncertainty simulation including multi uncertain parameters is proposed.The statistical character for the simulation results is obtained and compared to the analytic solutions.The results validate the effectiveness of the method.On this basis,the multi-dimensional gPC is applied in the uncertainty simulation for shipboard IEPS.The uncertainty simulation for the propulsion system in line-start and normal ahead conditions is carried out.An approach which can be used to obtain the polynomial chaos expansion for non-polynomial terms by inverse matrix is proposed.Then the uncertainty simulation for the propulsion system with different operating conditions is achieved.The achievements of this thesis which can provide powerful simulation and analysis tool for the design and development of shipboard MVDC IEPS which possess important meaning in theory and engineering practice.Some research achievement can be applied in the simulation and stability analysis of other power systems.