Research On Three-phase Three-wire Intermediate Frequency VIENNA Rectifier

With the improvement of power factor and total harmonic content of three-phase rectifier in aviation applications,traditional passive FPC can not meet the requirements.In this paper,combined with the requirements of small and medium power rectifier in aviation,the research object is the three-phase three-wire VIENNA rectifier with intermediate frequency input.The working process,the design of voltage and current double closed-loop PI controller,the principle of input current single-cycle controller and the realization method of SVPWM are mainly studied.The causes of current distortion under IF input are analyzed in principle,and two innovative waveform improvement methods are proposed.The feasibility of control strategy and modulation strategy is verified by simulation and experiment.The specific research contents are as follows:1.The working process of VIENNA rectifier is analyzed in detail,and the rectifier model based on large signal is completed.The parameters of double closed-loop PI controller based on d_q synchronous rotating coordinate system are designed.The core control equation of single-cycle control theory is deduced.The realization method of single-cycle control is introduced.A simulation model is built in MATLAB to verify the feasibility of the two control methods.2.The relationship between voltage vector hexagon and switching state hexagon in SVPWM implementation of VIENNA rectifier is analyzed.In order to simplify the software implementation of space vector modulation,the implementation steps of SVPWM in non-orthogonal g-h coordinates are given in detail.This paper analyses the reason why the input current of VIENNA rectifier is distorted at the zero-crossing point due to the inductance voltage drop which can not be neglected under the intermediate frequency input.An improved modulation strategy is proposed to discard some small vectors and use input current to assist in judging the large sector of SVPWM.Aiming at the problem that input current sampling is easily disturbed in practical engineering application,a filtering method combining hardware and software is proposed.Improve the accuracy of sector judgment.Furthermore,according to the relationship between voltage utilization ratio and modulation ratio of SVPWM,the applicable conditions of input current aided judgment method for large sector of SVPWM are analyzed,and the output voltage boundary conditions using this method are obtained.The principle and implementation process of the two methods are introduced in detail.The correctness of modulation method and waveform improvement strategy is verified by simulation.3.The experimental platform of VIENNA rectifier is built according to the design requirements.The design process and selection method of input filter inductor,DC output capacitor and power device are given.The software architecture of the system is introduced.The execution process of the software and the methods of improving the software efficiency and control frequency are analyzed.Finally,the validity of the two control methods of the rectifier is verified on the experimental platform.At the same time,the validity of the SVPWM modulation method and the waveform improvement strategy is verified through the experiment.