Research On Optimal Design Of Brushless Doubly-fed Machine Based On Special Reluctance Rotor

Recent years have seen the gradual exhaustion of non-renewable resources, so the issueof energy is being highly focused all around the world. To solve energy problems, twomeasures need to be taken: one is to increase the efficiency of current energy through variouskinds of energy saving and emission reduction practices in order to prolong the use of currentenergy; the other is to seek all kinds of renewable energy and make use of them by reliablemeans so as to replace the current non-renewable resources step by step. For the time being,solar energy and wind energy are mainly regarded as the two renewable resources available,from which electric power can be transformed and then transmitted to electrical equipments.Thus, study on solar and wind energy has become a hot topic for researchers recently.In the field of wind power, doubly-fed machine has always played a key role. Up tonow, it is still considered as the optimal scheme for variable speed constant frequencygenerator of intermediate and high power. However, since the exciting winding of rotor canbe only connected with frequency conversion equipment through brush, its reliability is thushugely affected. Moreover, daily maintenance becomes more complex as a result of brush.These problems are so important as to be able to determine whether wind power can come tothe grid in low cost. Under the circumstances, the study of brushless doubly-fed machine hasgradually drawn people's attention. Its theory is similar to that of traditional doubly-fedmachine, in which both can achieve variable speed constant frequency(VSCF) generation, andtheir main power winding can generate full load in lower transducer power. A particularfeature of brushless doubly-fed machine is that the exciting winding of rotor is removed,instead two sets of windings are fixed on stator, as a result, the elimination of brush and slipring can actively promote the development of variable speed constant frequency(VSCF)generation system.Brushless doubly-fed reluctance rotor machine (BDFRM), due to its simplemanufacturing process and high reliability, has become the hotspot of electrical machine ofsimilar kind. Since no report has been given on optimal design of this kind of machine so far,it is of significance to study it. The dissertation therefore sets BDFRM as its research objectand works out a complete optimal design for it. At first, the working principles of brushless doubly-fed machine is introduced andexplored in the dissertation. Then based on traditional study of motor, emphasizing thespecialty of brushless doubly-fed reluctance rotor machine, its working machamism iselaborated and a mathematical model is deduced to describe it accurately. The design ofprototype is made according to the structure characteristics of the machine, such as the shapefeatures of stator and rotor, winding style, special demand for mechanical structurecomposition, etc. Starting from these questions, the dissertation analyses the structure featuresof BDFRM, then gives preliminary design of its prototype by making reference to traditionalinduction motor design process, and finally obtains some design results such as parameters ofmotor external dimensions.In any study of new type motor, the winding inductance calculation is of greatimportance. The research of BDFRM makes no exception. Based on some common methodsused for motor inductance parameters, the dissertation proposes to improve winding functionso as to make its result closer to the true value, which can be applied directly to motor design.In addition, its calculation is much faster than finite element method so that time can beshortened vastly in the applications of designing of the motor.After obtaining motor preliminary design parameters, the motor dimension, statorpunching shape, stator winding type and rotor pole width can be determined. In the prototype,axial lamination rotor with flux barrier is used possessing advantages of simple manufacturingprocess and solid structure shared by common reluctance rotor, and a unique performance ofbeing simulated to approach ALA rotor. There are many shape parameters involved in thisrotor design, mainly including various shape parameters of flux barrier and gap width, whichcan adjust and affect motor performance in small scope. It is believed the whole motoroptimal design can be achieved by setting a reasonable optimal object, and then finding asuitable optimal design method, as every shape parameter of special reluctance rotor producesits optimized one. On the basis of finite element calculation of dynamic electromagnetic field,the prototype generates its simulation model, and an optimal calculation method, Taguchimethod, is used in the design to deal with various shape parameters. Then the maximumaverage electromagnetic torque and the minimum torque ripple of same volume are set asoptimal objects, and16parameter combinations are soon produced using orthogonal table rule. Later an optimal combination is selected and multi-object and multi-parameter optimaldesign is finally achieved.At last, an experimental prototype is produced by using the optimal design results, andtested thoroughly at the state of synchronous generation, this test further verifies the validityof motor optimal design.