Research On The NPC/H Inverter With Equivalent 36-Pulse Rectifier

The multi-pulse rectifiers can increase the mumber of pulses of rectifier equipments by adopting the technology of phase-shifting and multipling rectification.To live up to the strict harmonic cancellation standards,more and more power equipment manufactures are adopting multi-pulse rectifiers,which greatly improves their application in the power electronics convert field.In this paper,a topology of equivalent 36-pulse rectifier which adopts the technology of compound phase-shifting and multipling rectification is analyzed.It achieves 36-pulse harmonic cancellation by reducing the number of the secondary wings of different structure,which makes the manufacture of phase shift transformers more convenient.By theoretical analysis,we can get the conclusion that the lowest harmonic order of the line side current is 35^th,the effect of its harmonic cancellation is ideal.One practical application of equivalent 36-pulse rectifier is to supply 3 DC voltages for the five-level NPC/H bridge inverter by packet connecting the output in series.In this paper,the factors which influence the total harmonic distortion(THD) of phase voltage and bring about the deviation of DC line voltages of five-level NPC inverter fed by equivalent 36-pulse rectifier under in-phase disposition modulation are also analyzed.The results of simulations under ideal and unideal conditions and experiments of low power load prove the favorable harmonic cancellation effect of equivalent 36-pulse rectifier and the correctness of theoretical analysis as well.Meanwhile,the relationship between the THD of phase voltage of five-level NPC/H bridge inverter and the deviation of DC line voltages and load condition,output frequency and the size of DC line capacitors is obtained.