Research On Series-Connected Multi-Pulse Rectification Technology Based On Power Electronic Transformer

The series-connected multi-pulse rectifier with the advantages of simple,reliable and double the output voltage,etc.It is suitable for high-voltage and high-power electric energy conversion occasions.The phase-shifting transformer which is heavy and occupy a large volume is a necessary component of the multi-pulse rectifie,resulting in a relatively low power density of the multi-pulse rectifier.To this end,this article takes the traditional series-connected 12-pulse rectifier as the basic topology,and studies the series-connected 12-pulse rectifier based on Power Electronic Transformer(PET).The study combines the power electronic transformer technology with the series-connected multi-pulse rectifier technology to improve the performance of the series-connected multi-pulse rectifier.In order to reduce the phase-shifting transformer’s volume and weight,a series-connected 12-pulse rectifier based on PET was studied.The working principle of the rectifier are analyzed.Using the switching function method,the conduction modes of the three-phase diode rectifier bridges are determined.According to the equivalent model of the rectifier,the operating modes are determined.The expression of PET input voltage was calculated.The suppression method of the voltage spike of the rectifier is studied.According to the calculation model of the rectifier,the expression of the input current of the rectifier is calculated.The simulation and experimental results show that power electronic converter can realize the frequency-up function,the method of suppressing voltage spike of the rectifier by the RCD buffer circuit is effective.The use of a high-frequency phase-shifting transformer instead of the power-frequency phase-shifting transformer can reduce the volume of the phase-shifting transformer by about two-thirds and improve the power density.In order to suppress the voltage spike of the rectifier and improve the symmetry of the input voltage waveform of the high-frequency transformer,the design and influence of the input inductance of the rectifier are studied.According to the requirements of rectifier power factor and filtering,the range of input inductance was calculated.According to the calculation model of rectifier,the expression of phase difference between AC input voltage and PET input voltage was calculated.The control signal of PET after eliminating the influence of p hase difference is designed.The simulation and experimental results prove that when a smaller inductance value is selected within the optimal inductance range,the voltage spike of the PET input voltage is significantly reduced.Using the PET control signal after eliminating the influence of the phase difference,the input voltage waveform of the high-frequency transformer is symmetric Sexuality has improved significantly.In order to improve the symmetry of the winding structure of the high-frequency phase-shifting transformer and the balance of leakage inductance distribution,a series 12-pulse rectifier using a high-frequency extended-edge star transformer was studied.According to the working principle of the rectifier,a high-frequency extended-edge star transformer is designed.Using the switching function method,the PET input voltage and the rectifier output voltage expression are calculated.According to the structure of the rectifier,the input current of the high-frequency extended-edge star transformer and the input current of the rectifier are calculated.The simulation results prove that the PET input voltage is 12 step waves,the ripple of load voltage and load current are very small.The high-frequency extended-edge star transformer can achieve the same phase-shifting effect as the original high-frequency Y/Δ/Y transformer.The symmetry of the winding structure of the high-frequency phase-shifting transformer and the balance of leakage inductance distribution are significantly improved.In order to reduce the complexity of PET and save the manufacturing cost of the rectifier,the low-complexity PET with a small number of devices was studied and applied to the series-connected 12-pulse rectifier.According to the working principle of the rectifier,the control circuit of PET is designed,and the working mode of the rectifier is analyzed.Using the switching function method,the expressions of the output voltage and current of the rectifier are calculated.The simulation results show that the PET control circuit is effective,and the switch tube and diode included in the PET are in high-frequency complementary conduction state.The two sets input voltage on the primary side of the high-frequency phase-shifting transformer is high-frequency alternating current with a phase difference of 180~o.Compared with the existing PET used in multi-pulse rectifier,the low-complexity PET uses fewer devices,the control circuit is simple,and it has higher reliability.