Research On Phase-Selection Control Rectification Technology Of Multiphase Electrically Excited Wind Generator

In order to give full play to the advantages of distributed energy,such as clean,renewable and large amount of resources,many experts at home and abroad put forward the concept of DC micro-grid which has the characteristics of small reactive power loss and easier to access for distributed power.In order to make full use of wind energy,improve efficiency and expand the operation range,compared with permanent magnet generators,this thesis adopts electric excitation generator whose AC side voltage can be adjusted.When the wind speed varies widely,by excitation PID regulation,the phase winding of generator output four different voltage levels in different speed intervals.Because the multiphase generator has the characteristic of multiple space voltage vectors,when the wind speed is small,the phase voltage of the machine is small,selecting two-phase conduction with a large difference in space voltage vector;when the wind speed is large,the phase voltage of the machine end is large,selecting two-phase conduction with a small difference in space voltage vector,and then the voltage amplitude between the DC side and the AC side is small,so that the DC voltage is constant after rectification under the action of the voltage stabilizing capacitor.This has important reference significance for maintaining the voltage stability of the micro-grid when the wind speed varies widely.Firstly,this thesis takes six-phase generator as an example to analyze the composition principle and rectification characteristics of six-phase shift 30°and 60'generators,and then designs a six-phase-shifted 60°generator by ANSOFT and verifies its stable and reliable operation by finite element analysis.Secondly,a new phase-selection control rectifier topology is designed,in which the converter is a six-phase rectifier bridge composed of diodes and thyristors.Through the selective turn-on and turn-off of the thyristors,the theory of phase-selection control rectifier for multiphase generator is put forward.At constant speed,several different voltage levels are output just by the phase-selection control,and the simulation model is built in Simulink to verify the feasibility and effectiveness of the phase-selection control theory.When the wind speed varies widely,the excitation PID control and the phase-selection control of the multiphase generator achieve the purpose of maintaining the DC side voltage stability after rectification.Thirdly,because the rectifier loads introduce the 5th and 7th harmonic current to the generator,the torque contains a large 6th harmonic torque,which is very unfavorable for the stable operation of the motor.On the basis of establishing the mathematical model for harmonic analysis,an attempt is made to inject a small 6th harmonic current into the rotor,and by adjusting the magnitude and phase of the 6th harmonic excitation current,the 5th and 7th harmonics introduced into the stator by the rectifier load maybe can be weakened or even eliminated.Finally,the effectiveness of the proposed harmonic elimination method is analyzed by designing the generator model in ANSOFT.