Research On Electromagnetic Characteristics And Transient Model Of Wound-Rotor Brushless Doubly-Fed Machine

The brushless doubly-fed machine (BDFM) is a novel induction machine in according with the requirement of speed regulation. The structure of the BDFM is similar to that of conventional induction machine. The BDFM can run at asynchronous mode, synchronous mode and doubly-fed mode. The BDFM eliminate the slip ring and brush, and has advanteges of simple structure, reliability, a fractionally rated converter and adjustable power converter. The BDFM is attractive as a variable-speed and constant-frequency generator and adjustable speed driver.The power winding and the control winding of the BDFM have no direct coupling, they couple by a special designed rotor. The rotor structure is the most important factor to the performance of the BDFM. The currently widely used types of rotor across the world are special cage, reluntance, wound-rotor and hybrid structures. Nowdays, the trial-manufactured prototype of BDFM upper to MW have the structures of special cage and wound rotor. The special cage rotor BDFM has the advantages of easiness of manufacture, robustness, but it has the shortages of low utilization ratio of conductors and abundant harmonics. Relatively speaking, the wound rotor BDFM has a more flexible arrangement of rotor winding; it makes the winding factor of two fundamental harmonics suitable and weakens the other harmonics at the same time. The wound rotor BDFM have superiorities of harmonic suppress and high efficiency.Research object of this dissertation is wound rotor BDFM, the theory and test of wound rotor BDFM are studied in depth. The main aims of the research are to verify the applicability of wound rotor structure designed with the principle of tooth harmonics and sinusoidal winding in high and medium capacity machine. More concise '?'-type equivalent circuit of the BDFM has been derived, and the transient model of BDFM has been constructed by the means of space vector. These make the performance analyze of the BDFM easy, and promote the application process.The main contents of this dissertation are concluded as follows:Firstly, the evolution process of the BDFM has been reviewed, the basic theory and operating pattern of the BDFM have been summed up, the relationships between main dimension and electromagnetic design parameters have been analyzed, and the importance of rotor winding design has been revealed. At the basis of these, the principle of tooth harmonics and sinusoidal-structure winding have been introduced emphatically, designing thoughts and methods of wound rotor winding have been depicted in detail, and relationships between two different pole-pair air flux density and composite magnetic field have been analyzed, and the relationship between air-gap magnetic field characteristics and different poles of the BDFM have been uncovered.Secondly, considering the basic features of the BDFM, the basic equivalent circuit of the BDFM has been deduced from the equivalent circuit of ordinary induction machine. At the basis of this, utilizing equivalent network transformation, the '?'-type equivalent circuit of the BDFM has been obtained, and the parameters of equivalenr circuit have been identified by the means of calculation via magnetic pass method and testing method with the mutual inductances of rotor winding decoupled in special operating condition. From the perspective of mutual inductance calculation, the combinating law of different poles of the BDFM has been summarized, and energy transfer relations at different operating mode have been analyzed using equivalent circuit.And then, the basic analysis model of wound rotor BDFM under the abc stationary reference frame is presented, and the the transient space vector model of the BDFM under arbitrary speed has been deduced from the basic model by the means of transformation with space vector, and the transient equivalent circuit is given out. Short circuit currents of the BDFM have been studied by means of the space vector model.At last, modeling and simulation of an 800kVA prototype machine of wound rotor BDFM have been conducted, and no-load starting test have been done. Current densities, magnetic flux densities, generating capacity and harmonics at different parts of the prototype are analyzed from the simulation results, and the feasibility of wound rotor structure in high-medium BDFM has been confirmed, and the simulation results at no-load starting condition have been compared with the testing outcome. To verify the validity of '?'-type equivalent circuit, calculating method of magnetic pass, and the testing method of obtaining parameters of equivalent circuit, combined test have been worked at a 64kVA wound rotor BDFM testing rig.