Research On D-Type Asymmetric 24-Pulse Auto-Transformer Rectifier Unit

Transformer Rectifier(TRU)and Autotransformer Rectifier(ATRU)are important secondary power supply equipment on the aircraft.The inverter’s 115 V 360~800Hz variable frequency AC power is converted into 28 V low voltage DC or 270 V high voltage DC power supply for DC load.The multi-pulse rectifier phase shifts the input three-phase AC voltage to obtain multiple sets of three-phase voltages,and then rectifies the multi-pulse DC output voltage through the rectifier bridge.The higher the pulse number,the lower the input side current harmonic content(THD),and the smaller the impact on the aircraft power system.The 24-pulse ATRU is small in size,light in weight,and low in input current THD.It can meet the requirements of the aviation power system for the power equipment without filtering.The existing 24-pulse ATRU system has complicated structure or difficult transformer winding,and the output voltage is not adjustable.The paper analyzes and compares the structure and performance of the existing 24-pulse ATRU.In order to solve the problem that the existing 24-pulse ATRU system is complicated and the output voltage is difficult to adjust,this paper focuses on the structural design and the method of buck-boost implementation of the D-type asymmetric 24-pulse autotransformer transformer.A D-type asymmetric 24-pulse autotransformer transformer structure is proposed.By reasonably designing the transformer winding coupling method and the relationship between the number of turns of the primary and secondary windings,four sets of three-phase voltages with different amplitudes are obtained,which make up 24 phase voltage vectors with the same amplitude and phase-difference of 15°,then across four rectifier bridges and convert into 24-pluse DC voltage,the output terminal does not need to balance the reactor;further,by increasing the primary side of each phase of the extension winding or intermediate tap and the secondary winding of each phase,at the same time changing the relationship between the number of turns of the primary and secondary windings and the position of the same name end,realizes the step-up and step-down adjustment of the output voltage.In this paper,the relationship between the turns of the primary and secondary windings of the autotransformer,the winding current and the equivalent capacity are derived.The effects of different output voltages on the structure,input and output performance and equivalent capacity of the transformer winding are analyzed.Finally,the simulation model is built in MATLAB/Simulink for simulation analysis,and the prototype of D-type asymmetric 24-pulse ATRU is developed.The experimental results verify the rationality and feasibility of the structure.