Solid State Transformer Rectifier Stage Equalizing Voltage And Power Method Research

Solid state transformer is also called as power electronic transformer,which contains the rectifier stage,the double active bridge(DAB)stage and the inverter stage.It is a kind of intelligent novel transformer,which combines power electronic conversion technology and high frequency conversion technology.Solid state transformer can achieve electrical isolation and voltage level conversion,and it has the advantages of small size,light weight,power factor correction,improving power quality,controlling flexibly voltage and power.In addition,it can provide grid connected interface for distributed energy sources,supply power for DC load and connect energy storage devices.Firstly,the carrier phase shifted SPWM modulation mode and the Fourier transform of this modulation mode is analyzed.The advantages of carrier phase shift modulation in multilevel circuit by harmonic decomposition has been verified.Illustrating the DAB soft switching operation process and deriving the condition of soft switching in DAB stage.Secondly,the mathematical model of three-phase module cascade SST rectifier stage and DAB stage control system is established,and the small signal analysis is performed.The common duty cycle control method based on dq0 transform is adopted in the rectifier stage,and input and output voltage following control method is adopted in the DAB stage.Then,aiming at the problems of voltage and power imbalance of the rectifier,two voltage and power balancing control methods are proposed.One is achieving voltage and power balance through rectifier stage and DAB stage coordination control.The other one is restructuring modulation wave vector,which can make the reactive power equal distribute,the active power distribute according to the demand.Finally,establishing the 10 KV SST simulation model with MATLAB/Simulink.Designing the 360 W experimental prototype.including the sampling conditioning circuit design,drive protection circuit design,device selection,high frequency transformer design.The simulation and experimental results show that the coordination control is simple and easy to implement,but the modulation ratio vector reconstruction control is complex and it is difficult to achieve.