Modelling And Electromagnetic Design Analysis Of Large Scale Doubly-fed Induction Generator-motor

Large Scale doubly-fed induction generator-motor(DFIGM)is a novel type of adjust-speed large scale machine for pumped storage plants and hydro plants.The DFIGM has many advantages,such as flexible power control,enhancement of power system stability,clean energy accommodating increasing,improvement of both effieciency and financial efficiency of unit.Thus,application of DFIGM can make significant benefits on modern power system characterized by clean,intelligentialize,integration,and marketilization.At present,the manufacture of first DFIGM in china has already been determined and the design work is going to be started.However,there are still a lot of deficiencies in the modelling and electromagnetic design technique of large scale DFIGM.And it is still worth advancing on the aspect of mathematical model and analysis,electromagnetic design,and optimum design method of DFIGM.As a consequence,for the purpose of critical design technique development,the researches on modelling,harmonic response analysis,parameters determination,electromagnetic design,and optimum design method of DFIGM are carried out.The corresponding calculation and design methods are presented.The feasibility and superiority of presented models and methods are validated by derivation,simulation,and experiment results.The necessity of the development of large scale adjust-speed generator/motor-generator technique is briefly summarized firstly.The developing history and research status of DFIGM are introduced.The deficiencies of existing researches on DFIGM design are proposed.And the significance,contents and methods of this dissertation are illustrated.The mathematical model of large scale DFIGM is developed based on the spiral vector theory to unified the steady-state,dynamic,and harmonic model.The steady-state current harmonic response characteristics,generated by electrical harmonic sources and mechanical speed variation are studied.The relationships between the properties of harmonic sources,the operation speed,and the response characteristics are revealed.The properties of dangerous harmonic sources are identified.The steady-state characteristics of output active and reactive power considering harmonic sources are studied.The relationship between power components and operation conditions is identified.And the physical properties of power components are revealed.The computation method of model parameters by finite element(FE)method.By estabilishing detailed leakage inductance model of DFIGM,the FE method is applied to extract the detailed inductances in different operation conditions.The presented method can cover the shortage of accuracy in analytical parameter formalations of novel machine in which the experiment results to correct the empirical coefficients are lacking.The sensitivities of model parameters are analysed,and the parameters whose variation should be considered in the accurate model are proposed.Based on the derivation currents in three-phase shortcut condition,a transient parameters calculation method is presented using FE and signal processing technique.The accuracy in transient parameters computation is improved by considering inductance parameters variation in transient process.A general analytical method of air gap potential function,which is suitable for all kinds of winding types for large scale DFIGM especially unconventional windings,is establishsed.Two fast computation method of complex relative permeability function,using Schwarz–Christoffel transformation and static electric field FE method respectively,are proposed.The advantages of presented model and method in both accuracy and calculation speed are validated.The analytical model to estimate electromagnetic parasitic force and mechanical response is developed.An analytical formulation and a FE method to calculate additional surface losses in slotted and laminated machine are presented.The tools of electromagnetic analysis and design are accomplished.The simulation model of DFIGM system is established.The ouput harmonic properties of rotor converter and the influences of output harmonics are analysed.The effects of operation points on machine characteristics are presented.The methods to eliminate the current harmonics are designed.And the improvements on machine design methods are proposed to consider current harmonics and influence of operation points.The potential harmonic propertis of different types of stator and rotor windings are analysed.The dangerous electromagnetic vibrations generated by winding potential harmonic propertis in different design of stator and rotor windings are identified.The optimum design methods of windings to eliminate the risks of vibration for winding types choosing and matching are proposed.The relationship between air gap length and machine characteristics when remains slot diamentions unchanged is analysed,which reveals the influence of slot permeability harmoncis on machine properties.A dual objective optimization method based on Pareto front technique to determine air gap length is proposed,to improve both technical and econimic efficiency in rated operation point.A novel method to improve the machine design by applying magnetic slot wedges and decreasing air gap length is also proposed.And the design of magnetic slot wedges is studied to validate the presented method.