Analysis Calculation And Experiment Research On Losses Of Brushless Doubly Fed Generator With Novel Hybrid Rotor

Brushless doubly fed generator(BDFG)is a new type of adjustable speed machine with special structure,and it has the advantages of without brush and slip ring,reliable operation,adjustable power factor,small required inverter capacity,etc.Therefore,BDFG has good development and application prospects in the variable speed constant frequency wind power generation field.However,BDFG has complex magnetic field and rich harmonics,result in the difficulty in calculation of losses.At present,there is still a lack of accurate analysis and calculation methods.In this paper,a 25 kW,8+4 pole BDFG with novel hybrid rotor is studied,and core loss,copper loss,mechanical loss and load stray loss of the generator are analyzed.The main research of the paper has been done as follows:(1)The stator and rotor structure feature,operating principle and magnetic field modulation mechanism of BDFG are introduced in detail.And the novel hybrid rotor structure BDFG with better coupling capacity,which consists of magnetic barrier and auxiliary cage,is analyzed in detail.The two-dimensional finite element analysis model of BDFG with hybrid rotor is established.Furthermore,the simulation analysis of the no-load and load characteristics of the generator is carried out.(2)Aiming at the problem of complex magnetic field,rich harmonic content and difficult calculation of iron loss in BDFG,an improved E&S model considering the effects of alternating magnetization,rotational magnetization and harmonic magnetic field is proposed.On the basis of the analysis of the magnetic density characteristics of tooth portion,yoke portion and radial direction and tangential magnetic layer of rotor,the classical core loss separation model,the orthogonal decomposition model and the improved E&S model are used to calculate core loss of BDFG with hybrid rotor,and the comparative analysis of three kinds of core loss calculation models is performed.(3)The rotor structures of BDFG with hybrid rotor is different from the conventional machine.The calculation of the stator copper loss is relatively easy,and the calculation of the rotor cage copper loss is complicated.In order to calculate the rotor copper loss,the equivalent circuit of rotor cage is established.Moreover,the mutual inductance between the two sets of windings and the rotor cage is calculated,and the current value of the cage is calculated based on the relationship between flux,inductance,current and electromotive force.Furthermore,the stator and rotor copper loss considering the effect of skin effect is obtained.The mechanical loss and stray loss of BDFG with hybrid rotor are analyzed and calculated.(4)The experimental platform of the prototype system is established,and the performance test of BDFG with hybrid rotor under the generator load state is carried out.The efficiency of the generator at different speeds and loads is tested,and the correctness and feasibility of losses calculation model are indirectly verified.