Research On Modelling Analysis And Electromagnetic Design Of Wound-Rotor Brushless Doubly-Fed Machine

The Brushless Doubly-Fed Machine (BDFM) is a novel AC induction machine. The structure of the BDFM is similar to that of traditional asynchronous machine and the BDFM can achieve multiplicate operation mode, such as asynchronous, synchronous and doubly-fed operation mode. The BDFM avoids the use of brush and slip ring and has some advantages for its simple structure, robustness, reliability, adjustable power factor and a fractional rated converter. It will have wide application in the control-frequency saving-energy adjustable speed drive (ASD) systems, for instance, the fan and pump load drives, and the constant-voltage constant-frequency (CVCF) variable speed generation (VSG) systems, such as ship shaft generator, water power and wind power generation.The key factor affecting the performance of the BDFM is the rotor structure. Presently, the rotors of BDFM have mainly adopted the special cage and reluctance structures across the whole world, but the special cage and reluctance structures have some disadvantages for their low winding conductor utilization ratio and abundant harmonic contents of the rotor. Compared to the special cage and reluctance rotor, the wound-rotor BDFM studied in this dissertation has better performance index and practicability since it has obtained a flexible connection, and makes the winding conductor utilization ratio high and harmonic contents low by rational design, adjustment and control.With the object of wound-rotor BDFM, the research aims to study the theory of wound-rotor BDFM in depth, develop the effective mathematical model and equivalent circuit, write the convenient, reliable and accurate electromagnetic design calculation program and accelerate the progress of utilizing the wound-rotor BDFM.The main content of this dissertation is summarized as follows:First of all, this dissertation has summarized the principle, winding structure and operation mode of wound-rotor BDFM based on the review of the development of the research on the BDFM done by the national and international scholars. The summary lays its emphasis on the theory of the machine stator and rotor winding design. The general design method and connection of the stator and rotor winding is presented and the magnetic field analysis of the stator and rotor winding is studied in the dissertation.Secondly, the analysis model of wound-rotor BDFM under the abc stationary reference frame is given out and the fundamental equivalent circuit and various calculation formulas of the electromagnetic torque are obtained by deriving the analysis model of the machine under an arbitrary dqn reference frame via transforming the coordinate in the dissertation. Based on this, the chain equivalent circuit which is used for analyzing the harmonic effect on the performance of the machine is presented. Moreover, the small signal model which is used for the stability analysis of the machine is established to obtain the condition of a stable operation of the machine and the input condition is analyzed according to various control strategies. Further, the stability condition under the open-loop voltage control and the machine parameter effects on the stability are also studied in the dissertation.Thirdly, the problems in general principle of wound-rotor BDFM, such as the distribution relation of the power and capacity, the choice of the pole-pairs number, the confirmation of the main dimension and the choice of the electromagnetic loadings, are studied. The electromagnetic design flow chart of the machine and the calculation program developed by using the software of Visual C++6.0 are presented, and the calculation method and program function for each part of the electromagnetic design is illustrated. Additionally, the calculation formula, experimental measure method and estimation method of the machine parameter are raised, too.Finally, a prototype machine of wound-rotor BDFM with YZR200L frame size and 7/5 pole pairs is designed and the equivalent circuit parameters of the prototype machine are calculated. The performances of the machine under varied operation modes are studied by the simulation and experiment. The calculated and the experimental data have shown that the proposed mathematical model, equivalent circuit and electromagnetic design calculation program are validated.