Digital Control And Implementation Of Aero Variable Frequency Three-phase Buck-type Rectifier

With the advantages of high fuel-efficiency,high reliability and low maintenance cost,more electric aircraft is gradually dominating the modern aviation industry.As an important device for converting AC energy to DC energy in aviation variable frequency generator,the three-phase Buck rectifier has great research value.Along with the upgrade of aero equipment,a large number of non-linear loads have introduced more harmonics,which makes electrical equipment have higher requirements for power grid quality,the industry began to adopt rectifiers with Power Factor Correction(PFC)technology to reduce the input current Total Harmonic Distortion(THD).However,limited by electronic components,modulation technology and control technology,the key technology of the three-phase Buck rectifier is still mastered by foreign companies,which exists the risk of the “stuck neck”.Once the relevant enterprises cut off the supply,China’s aviation industry will suffer huge loss.So,this thesis researches on the high-performance aviation variable frequency three-phase buck rectifier,focusing on the control technology under high switching frequency.The specific research contents are as follows:Firstly,this thesis studied the three-phase buck-type rectifier with two-stage.Analyzed the operating principle of the front-stage three-phase buck-type PFC rectifier and built up the mathematical model.Models includes three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating system,and equivalent circuit models control block diagram are given.Analyzed the operating principle of the post-stage isolated half-bridge converter,and derived the turns ratio of the transformer.Based on the mathematical model established above,this thesis designed a hardware circuit under high switching frequency.Derived the device parameters of input LC filter,common-mode filter and output LC filter in the main topology,and designed the micro control unit(MCU)circuit,driving circuit,sampling and signal conditioning circuit,power supply circuit,protection circuit and other related hardware circuits.The algorithm flow of control software algorithm is given.Based on the designed hardware circuit,designed the digital control system of the three-phase Buck rectifier.Based on the twelve-sector five-segment space vector PWM(SVPWM)modulation strategy,derived the fundamental current vector magnitude and vector action time inside each sector.Based on the dual-loop PI controller,designed the corresponding DC voltage outer-loop and DC current inner-loop controllers and derived the digital control system equations.Built the corresponding simulation models on the MATLAB/Simulink platform,and the simulation results verify that the designed control system can achieve the input current total harmonic distortion below 5% and a power factor(PF)>0.99 in a wide frequency range(50Hz～400Hz).Finally,based on the designed hardware circuit scheme and simulation model built,the thesis establishes a 750 W experimental prototype.Experimented under different input frequency,and the test results showed the effectiveness of the designed control algorithm.