Research On Parallel Multi-pulse Rectification Technology Based On Harmonic Blocking Reactor

The parallel multi-pulse rectifier has the advantages of simple structure,high reliability and high working efficiency,and wide applications in many fields,but the traditional parallel multi-pulse rectifier cannot suppress the Non-featured subharmonic such as 5th and 7th generated when the input voltage is unbalanced.Based on the parallel 12-pulse rectifier,this paper studies the voltage and current characteristics of the parallel 12-pulse rectifier when the input is unbalanced,the 12-pulse rectifier based on the harmonic blocking reactor,the 24-pulse rectifier based on the passive harmonic blocking reactor and the multi-pulse rectifier based on the active harmonic blocking reactor.Furthermore,it analyzes its adaptability to the load changes,which is of great significance for improving the power quality and maintaining the stable operation of multi-pulse rectifiers.In order to analyze the input and output characteristics of the paralle l multi-pulse rectifier when the input voltage is imbalanced,the parallel 12-pulse rectifier with the triangular autotransformer is studied when the input voltage is imbalanced.The topology of the transformer and the operating principle of the rectifier has been analyzed.According to the basic theorem of the circuit and the Fourier series,the load voltage and input current under unbalanced conditions has been calculated.The ripple factor of the output voltage and the harmonic components of the input current has been analyzed.The simulation and experimental results show that the non-characteristic subharmonics such as 5th and 7th generated by the rectifier are the main cause of the power quality degradation when the input voltage is unbalanced.In order to suppress the non-characteristic subharmonics in the rectifier circuit when the input voltage is imbalanced,a 12-pulse rectifier circuit based on the passive harmonic blocking reactors has been proposed.According to the law of electromagnetic induction,the topology and operating principle of the passive harmonic blocking reactors has been analyzed.According to the structure of the transformer windings,the expression of the input current has been derived from the perspective of the minimum input current THD value.The voltage on the harmonic blocking reactors has been calculated and the conduction mode of the rectifier bridge has been determined.The simulation and experimental results show that the passive harmonic blocking reactors have significant effects on the suppression of non-characteristic subharmonics such as 5th and 7th,which can effectively improve the power quality..In order to suppress the characteristic subharmonics dominated by 12 k±1 harmonics in the rectifier circuit,a parallel 24-pulse rectifier based on the harmonic blocking reactors and a parallel multi-pulse rectifier based on the active harmonic blocking reactors are proposed.The topology of the 24-pulse rectifier based on the harmonic blocking reactors has been analyzed.The expression of rectifier input current has been calculated.The simulation results show that the input current of the rectifier is 24 stepped wave,and its spectrum only contains 24 k±1 harmonic.The topology of multi-pulse rectifier based on active harmonic blocking reactors has been analyzed.The corresponding control circuit has been designed.The simulation results show that the input current THD value of the rectifier can be reduced to 5.37% after using the active harmonic blocking reactors.Harmonic suppression effect is obvious.In order to analyze the adaptability of multi-pulse rectifiers using harmonic blocking reactors to load changes,The change of the operating characteristics of the rectifier during the gradual change of the inductance load,the g radual change of the resistive load and the sudden change of the load resistance has been studied.The simulation results show that under the conditions of resistive load and inductance load,both the load voltage of the multi-pulse rectifier based on the passive harmonic blocking reactors and the THD value of the input current can be stabilized in a certain range regardless of the load creep or sudden change.Load adaptability is stable.The multi-pulse rectifier based on the active harmonic suppression re actor has a weak adaptability to the load gradual change,but when the load change is abrupt,the rectifier can quickly reach a steady state as well.