Research Of Several Key Techniques In Brushless Doubly Fed Machine

The brushless doubly-fed machine(BDFM)eliminated the slip ring which improves the reliability of the system,reduces the required capacity of the inverter and the cost of the system.This kind of motor has good application prospect in the field of variable-speed constant-frequency constant-voltage power generation and fits the large-capacity frequency conversion system.Based on the research topic of the National Natural Science Foundation of China and the Power Quality Engineering Research Center of the Ministry of Education of Anhui University,this paper analyzes and studies several key technologies of BDFM.The content mainly includes the following aspects:Firstly,in this paper,the operating principle of the BDFM is analyzed.the expressions of the stabilized speed and the slip rate are deduced,the magnetic field modulation mechanisms of the wound rotor and reluctance rotor BDFM are separately derived,and the magnetic field modulation mechanism of the new hybrid rotor BDFM is also derived based on that,theoretically proved that the magnetic field modulation of the new hybrid rotor BDFM is the superposition of the two formers.Secondly,in order to solve the problems of the high rotor harmonic content and the low utilization rate of the conductor,based on the "tooth harmonic" principle,a BDFM using concentric rotor windings with different turns of coil is proposed.The paper analyzed the design principle of the winding,deduced the calculation formula of harmonic magnetomotive force,derived the expression of the distribution coefficient which is suitable for all kinds of winding.The calculation example was given based on the sample,and the finite element method was used to study the performance of the novel BDFM,the result has been compared with other different motors included reluctance rotor BDFM,five league turns winding rotor BDFM and special cage rotor BDFM performance,proved that the proposed concentric rotor BDFM with different number of coil turns has low harmonic contents and high utilization rate of conductor with excellent performance.Then,based on the new type of hybrid rotor BDFM proposed in chapter 2,the magnetoresistive effect and the electromagnetic performance of the BDFM when the rotor side has no windings are analyzed by using the finite element method.And the structure of the motor is optimized,compared the motor characteristics of using hybrid rotor and double sine winding rotor,the results showed that the new hybrid rotor BDFM has many advantages in the magnetic field modulation capability.Then,based on the equivalent circuit of the wound rotor BDFM,the relationship among the rotor current,the output phase voltage of the power winding and the excitation current of the control winding under no-load and load conditions,as well as the relationship between the system output power and the excitation current of the control winding under load conditions are deduced.The finite element method was used to study the performance of 2/4 and 1/3 pole-pairs motor respectively under the combination of two pole-pairs,which provided a theoretical basis for the choice of power winding and control winding of the BDFM when determining the pole-pairs.Finally,setting a 64 k W,2/4 pole-pairs concentric rotor BDFM and a 30 k W,1/3 pole-pairs new hybrid rotor BDFM with different turns of coil as test model,we tested the generator voltage of the two power windings under different speed with no load and the voltage,the frequency and the voltage waveform distortion rate power winding under different load,as well as the voltage and current changing curves of different windings(PW and CW).And the test between the 5 pairs of equal turns winding and the hybrid rotor are proceeded,the results of phase voltage and excitation current of the power windings with the pole pairs of the power windings and the control windings exchanging are given.