Modeling And Finite-Element Method Simulation Of Brushless Doubly-fed Machine

Brushless Doubly-fed Machine (BDFM), as a novel machine without slip ring and brush, retains much of the simplicity, robustness and reliability of cage-rotor induction motor, but may achieve asynchronous, synchronous and doubly-fed operation mode just like a conventional wound-rotor induction motor. However, because of the special configuration and the complexity in the mathematical model and electromagnetic designing of BDFM, there is not, as far as information goes, any report about commercial product series of BDFM, and nor reference about detail design program and procedure suitable for the design of BDFM. Therefore, it is a challenge task to continue related researches so as to develop a convenient, reliable and accurate software package for BDFM. It is the purpose of this dissertation's attempting.With the object of cage-rotor BDFM, the basic theory, finite-element method (FEM) simulation, and parameters calculation of BDFM are investigated. Particularly, by the means of the reprogramable functions in the powerful commercial software ANSYS, 3 software package proposed in this dissertation for parameter calculation and for the steady-state performance and transient performance are developed. The packages are valuable in practice for the simulation and the design of BDFM.The main content of this dissertation is summarized as follows.(1) Based on comprehended references, a review of development progress of BDFM, including operation principle, analysis methods, characteristics simulation, parameters calculation, FEM simulation model etc. is summarized to present research information at home and abroad. The summary presentation puts emphasis on basic models of BDFM such as multiple coupled circuit model, and d-q model.(2) Under the circumstance of software ANSYS, a magnetic-circuit coupled pseudo-stationary FEM model for eddy current field is proposed and the corresponding package is developed so as to calculate the steady-state characteristics of BDFM. Besides, the magnetic-circuit coupled time-stepping FEM suitable to simulation of the dynamic behaviors of BDFM is also developed. Both models are programmed in APDL ( ANSYS Parametric Design Language ).Since the configuration of BDFM is quite different from the common alternating motors, very important is to have a suitable FEM model instead of the methods used recently for fast and accurate calculation of the steady-state performance. The proposed magnetic-circuit coupled pseudo-stationary FEM model is able to meet the demand. Without any special treatment of the moving rotor, the model is applicable for simulation the steady-state characteristics of BDFM at different slip, in which not only the saturation effect and skin effect are taken into account directly by the field mathematic model, but also some 3-D field effects such as the end effects of slip ring are considered by the way of traditional parameter calculation.The other FEM model proposed here is based on time-stepping FEM model, which is applicable for analysis of both transient and steady-state performances of BDFM. The incomparable advantage of the model is its fine accuracy because the minimum presumptions are used for the model set up, although much longer the computing time is needed. The developed algorithm contains coupled magnetic field-circuit equations. To deal with the moving rotor, the method of interpolating moving boundaries, combining constraints and the shape function to interrelate the vector potentials at the corresponding boundaries, are adopted in programming so that all the complicated re-mesh processing at each time step is totally avoided.The experiment results show that both proposed models are available for calculation of the steady-state performance of the machine operated in asynchronous, synchronous and doubly-fed mode.(3) Methods to calculate parameters of BDFM are investigated in Chapter 5. An enhanced energy perturbation method is proposed, and, then, the related program is achieved.Self inductors and mutual inductors of the windings are important parameters for analysis of performances as well as for the design of the motor. A nonlinear inductor may be expressed as either secant inductor, which is defined as that flux linkage is divided by current, or differential inductor defined as that the increment of flux linkage is divided by the increment of current. The later is usually adopted in a deferential circuit equation. The method of winding function in circuit analyzing is suitable for calculation of linear or secant inductor but differential inductor. The analytical formulas for linear inductors of BDFM are derived by the method of wingding function. For the calculation of differential inductor, an enhanced energy perturbation method is proposed. The advantages over conventional energy perturbation method are those: higher computing efficiency as lower iteration, higher accuracy as direct calculating of energy perturbation and only first derivation used, bigger current perturbation allowed, without re-mesh processing in the calculation of mutual inductors between stator winding and rotor's loops.(4) The principles for the design of BDFM are summarized, looking back development of the design methods for traditional alternate machines and looking around the design principles for BDFM in references. A prototype BDFM is made and some basic experiments are tested.