Research On Quasi-Z Source Direct Matrix Converter For Asymmetrical Six-Phase Induction Motor

Multiphase machine drive system can achieve high power at low voltage and have merits of high reliability and control flexibility.Given this,it has been increasingly applied to the field of high-power AC drives,such as modern industrial equipment,ship electric propulsion and locomotive traction.Aiming at the characteristics of asymmetrical six-phase induction motor in multiphase machines,this paper's research mainly concentrates on the core of drive system-power converter and its control strategy.The traditional six-phase converter has lower utilization rate to the input source voltage,so the output voltage is lower.When the input voltage changes in a wide range,the drive ability will decrease,and the anti-interference ability is poor.Also,compared to the three-phase system,the control strategy is more complex,and the tedious dead-zone setting has certain influence on the output waveform.At present,the general solution is to increase the DC/AC bus voltage by adding a step-up converter or AC voltage regulator on the input side,which not only increases the complexity and cost of the system,but also reduces the conversion efficiency of the electric energy.In this paper,the quasi-Z source(QZS)network proposed in recent years is introduced into the six-phase converter.With its unique impedance characteristics,many shortcomings of traditional multiphase converter such as low voltage transfer ratio can be solved.Considering the relevant researches about the Z-source multiphase converter are poor,the study in this paper can provide a preliminary exploration.Starting from the application object,this paper analyzes the working principle of asymmetric six-phase induction motor and establishes its mathematical model.The principle of coordinate transformation of six dimensional vector in six-phase system is introduced in detail,and its decoupled mathematical model is established in the stationary coordinate system(?-?)and rotating coordinate system(d-q).The simulation model of asymmetric six-phase induction motor is built based on the Matlab/Simulink platform to verify the correctness of the mathematical model and analyze its work characteristics through the results.Secondly,the quasi-Z source network is introduced into the six-phase inverter to form a Quasi-Z source six-phase inverter(QZS-SL-VSI),and its working principle is presented.In order to suppress the six-phase motor stator current harmonics,a SVM method which constructs the middle vector through the maximum four vectors is presented.On the basis of this,a dual voltage SVM modulation strategy and switch modes for the QZS-SL-VSI are presented.Through detailed simulation and prototype experiment,the output boost characteristics of the system and the effect of waveforms can be acquired to verify the feasibility of the method.Thirdly,an improved three-phase quasi-Z source is introduced into the input side of the three-phase matrix converter to form a quasi-Z source three-phase direct matrix converter(QZS-DMC).The working principle is introduced in detail and an improved direct SVM method with shoot-through zero vector is proposed.Also,the switching time sequence is analyzed.A detailed simulation comparison and a preliminary experiment are carried out to obtain the effect of input,output and voltage transfer ratio of QZS-DMC.Finally,on the basis of three-phase system,the quasi-Z source is introduced into the input side of the six-phase direct matrix converter to form a quasi-Z source six-phase direct matrix converter(QZS-SP-DMC)topology.Considering the complexity of multiphase DMC SVM method,a novel multiphase pulse width amplitude modulation(MP-PWAM)strategy is proposed,which can reduce switching losses and improve voltage transfer ratio.The system simulation model is established,and the effect of step-up voltage and frequency conversion is obtained.Then,the feasibility of the proposed structure and method is verified.