Research On Control Strategy Of Three-Phase Buck-Type PFC Rectifier With Wide Input Range

The three-phase buck-type PFC rectifier has been widely used in aviation power supply,electric vehicle charging system,high-voltage DC UPS power supply system,due to its wide output voltage range,limiting short-circuit current,no pre-charge circuit required for higher efficiency.At present,the research of three-phase buck-type PFC rectifier is mainly based on grid-side voltage rated input.However,in practical applications,the grid-side voltage varies widely.Therefore,this paper studies the control strategy of three-phase buck-type PFC rectifier which is suitable for wide input voltage range and wide input frequency range.Firstly,this paper analyzes the topology structure and working principle of three-phase buck-type PFC rectifier,and establishes the mathematical models in three-phase static coordinate system,two-phase static coordinate system and two-phase rotating coordinate system,which provides the theoretical basis for the control strategy research.Based on the twelve-sector five-segment SVPWM modulation strategy,the expression of the basic current vector working time in each sector is derived,and the overmodulation phenomenon of currentmode SVPWM is analyzed.The expression of the grid-side input current and the rotation track of the target current vector are derived when the overmodulation occurs.Then,through simulation,the influence of overmodulation on input current total harmonic distortion(THD)and inductance current at DC side of rectifier is verified.The simulation results show,although overmodulation can enlarge the output voltage range of the rectifier,it will introduce a lot of low-frequency harmonics of the grid-side input current.So overmodulation should be avoided in the research of three-phase buck-type PFC rectifier.The control strategy of three-phase buck-type PFC rectifier with wide input range is emphatically studied.A double closed-loop indirect current control strategy based on the threephase static coordinate system is studied.Thus,coordinate transformation and phase-locked loop(PLL)is neglected,and the instantaneous value of the input voltage at the AC side is sampled to calculate the duty cycle of the switch on time,so it is suitable for the three-phase buck-type PFC rectifier with wide frequency input.Based on the indirect current control strategy,a wide voltage input control strategy with variable output voltage reference value is studied,and the influence of wide range transient of input voltage on the rectifier is analyzed.The analysis results show that the transient of input voltage will lead to the overmodulation problem when the reference value of output voltage is different,and the double closed-loop PI control cannot effectively suppress the overmodulation.Therefore,a predictive compensation algorithm which directly affects the duty cycle is studied.Then,according to the algorithm,simulation model is built,which verifies the performance of the wide input three-phase bucktype PFC rectifier.Finally,the voltage stress,current stress of rectifier power devices and input,output LC filter parameters are derived,and an 800 W experimental prototype is built.The experimental results show that the indirect current control strategy studied in this paper can ensure that the three-phase buck-type PFC rectifier has the good performance of high-power-factor,low total harmonic distortion of input current,and high efficiency,when the voltage input range is wide(80vac ～ 140 vac,50Hz ～ 800Hz).Also,it verifies the working characteristics of the rectifier when Input frequency transient or input voltage transient and the predictive compensation algorithm can suppress the over modulation phenomenon when the input voltage is in a wide range of transient drop.