Design And Safety Analysis Of Step-up And Step-down 24-pulse ATRU Without Interphase Reactors

In civil aircraft flight tests,to complete test items and measure a large number of test data,test system added in aircraft is complex.Thus,the reliability of power supply system for trial-flight is highly demanded.Reliable operation of power supply system for trial-flight is one of the necessary conditions to ensure the success of flight test.Based on the international industrial standard SAE ARP4761,the concept of safety assessment is applied in the design of HVDC channel of power supply system for trial-flight.In this paper,Functional Hazard Assessment(FHA),Preliminary System Security Assessment(PSSA)and System Security Assessment(SSA)of HVDC channel are studied.In the process of PSSA,24-pulse autotransformer rectifier(ATRU)is used as AC-DC conversion unit in HVDC channel.Aiming at the problem that 24-pulse ATRU can not reach the failure probability index,two schemes are proposed to reduce the failure probability of HVDC channel.The schemes are as follows: adding non-similar redundant units to improve the reliability of HVDC channel,and using improved high reliability ATRU as AC-DC conversion unit.The reason why 24-pulse ATRU does not meet the failure probability index is studied.A step-up and step-down 24-pulse ATRU without interphase reactors is proposed.The connections and turns ratios among transformer windings are well designed.A 15-degree phase difference is formed between two of the 24 voltage vectors produced by the transformer,which makes the four rectifier bridge groups produce a 24-pulse DC voltage without interphase reactors.Meanwhile,by adding extended winding to each phase of the transformer,wide-range regulation of the ATRU output voltage can be realized.An ATRU prototype with a step-down ratio of 0.8 is developed,and the performance and environmental experiments of ATRU are carried out.Notch filters are designed to suppress the conducted interference in view of the problem that the conducted interference of power line exceeds the limit.Device selection is carried out and the reliability values of the two schemes are calculated.In the SSA,Failure Mode and Effect Analysis(FMEA)and Fault Tree Analysis(FTA)are used to verify the reliability of the two schemes,and some suggestions are given to improve the reliability of the two schemes.The output voltage of the new 24-pulse ATRU can be regulated in a wide range.Thus,the ATRU can be applicable to various DC power supply fields powered by three-phase mains.The safety evaluation process of trial-flight power supply system studied and implemented in this paper can be used as a reference for safety evaluation of other aircraft systems.