航空Vienna整流器缺相控制方法

A Lack Phase Control Strategy for Aircraft Vienna Rectifier

Vienna整流器因其高功率密度、高可靠性等优点,适用于多电飞机的交流供电系统。航空电网对可靠性有很高的要求,需要考虑电网不平衡甚至缺相故障的情况。当电网出现三相不平衡情况时,需要采取合适的控制方法消除电网负序分量对整流器输入输出性能的影响。而当电网出现缺相故障时,常规的三相控制方法失效,整流器通常需要停机保护,但降低了供电系统的可靠性。为了使整流器在电网缺相故障下维持输出功能,该文通过分析缺相状态下Vienna整流器的工作模态,提出一种单相空间矢量脉宽调制方法,并设计相应的控制环路,使得Vienna整流器在缺相状态下能够维持稳定的直流输出,并同时给出一种缺相判断方法。通过仿真和实验验证了所提Vienna整流器缺相控制方法的有效性。

Vienna rectifier is one of the most potential topologies for aircraft electrical systems due to its high power density,high efficiency,and high reliability.With the onboard electrical equipment increasing,the electrical power consumption increases significantly in more-electrical aircraft,resulting in harmonics and grid unbalanced issues in aircraft electrical systems.Three-phase rectifiers must maintain stable operation under unbalanced grid and lack phase condition,which presents a challenge to the control strategy of the Vienna rectifier.According to the instantaneous symmetrical component,the unbalanced grid voltage comprises fundamental positive-,negative-and zero-sequence components.The negative-sequence component leads to second-harmonic ripples in dc-link voltage and low-order harmonics in input currents.The mathematical model of the Vienna rectifier under unbalanced conditions is derived.DSOGI-PLL is utilized to calculate positive-and negative-sequence components of the grid and generate current references.In this way,input current harmonics and dc-link voltage ripples are suppressed well under the unbalanced grid.For higher reliability requirements,the application under the grid lack phase should be considered.Under a lack-phase grid,the conventional three-phase control strategy is invalid.Rectifiers usually detect the lack-phase fault condition and shutdown for protection,which decreases the reliability of the electrical system.In order to make Vienna rectifiers maintain stable output under a lack-phase grid,this paper first analyzes the mathematical model.The rectifier under the lack-phase grid is regarded as a single-phase PWM rectifier.By analyzing operational modes,a single-phase space vector pulse width modulation method is proposed,and the implementation process is introduced in detail.Different operational modes can be seen as seven basic voltage vectors,divided into zero,short,and long vectors according to the vector length.Like conventional three-phase space vector modulation,seven basic voltage vectors are used to synthesize the reference voltage vector.Not all switch combinations for each vector can be achieved at each moment,and four sectors are divided for exact synthetization.The dwell time for each basic vector satisfies the voltage-second balance principle.The vectors sequence is selected to be a five-segment form for minimizing the switching loss.The voltage of output capacitors can be balanced by adjusting the dwell times of a pair of redundant short vectors.Furthermore,according to the three-phase voltage sampling conditions under a lack-phase grid,a lack-phase fault detection method based on the phase locked loop is proposed.Different grid fault conditions can be determined by calculating the positive-and negative-sequence components of sampling grid voltages.The corresponding control loop is also designed for stable dc output under lack-phase conditions.If the grid voltages are three-phase input,a control strategy for the unbalanced grid is applied.If a lack-phase fault occurs,the corresponding control strategy is switched for lack phase control.A 4.5 kW aircraft Vienna rectifier prototype is built to verify the proposed control strategy.Experiment results prove that the Vienna rectifier can maintain stable operation under the unbalanced grid and lack-phase grid with the proposed control strategy.