| As the interface between power grid and industrial electronic equipment,the time-varying and strong non-linear characteristics of the industrial frequency rectifier will cause harmonic pollution to the power grid and bring serious power quality problems,especially in high-power applications.Multi-pulse rectification(MPR)technology is one of the important ways to control the harmonic pollution of high-power rectifier system.Passive harmonic suppression method on DC-side of MPR has limited harmonic suppression capability and will increase the content of high-order harmonics while reducing low-order harmonics,while active harmonic suppression method has significant harmonic suppression effect,but cannot improve the output voltage ripple characteristics of MPR and requires large-capacity of active auxiliary circuit(AAC)and modulated circulating current peak.In order to reduce both input current harmonics and output voltage ripple in MPR,this paper weighs the power quality and other factors,combines the advantages of active and passive methods,and carries out the research hybrid harmonic suppression method on the DC-side of MPR by using the efficient modulation effect of inter-phase transformation technology.The basic input and output characteristics of the conventional 12-pulse rectifier are derived with the help of switching functions,and the modulation effect of the passive double-tapped inter-phase reactor on the output currents of the rectifier bridges are analyzed,and the numerical relationship between the total harmonic distortion of the grid-side input current and the tap turns ratio of the double-tapped inter-phase reactor is derived,and the optimal turn ratio is found.With the goal of no harmonics in the input current on the grid-side,the optimal conditions to be satisfied by the primary side circulating current of the active inter-phase reactor under the condition of large inductance are analyzed,and their effects on the voltage and current characteristics of the rectifier are given,which lay the foundation for the research of the hybrid harmonic suppression method.Based on the study of the harmonic suppression mechanism of active and passive methods,a hybrid harmonic suppression method based on active-tapped inter-phase reactor(AT-IPR)is proposed,and a new hybrid harmonic suppression rectifier is obtained.The operating modes of the rectifier are analyzed,the modulation effect of the AT-IPR on the input current and output voltage of the rectifier is described,and two hybrid harmonic suppression schemes based on different active circulating current compensation strategies are explored according to the DC-side circulating current compensation effects.The effects of different hybrid harmonic suppression schemes on the harmonic of input current,ripple of output voltage,k VA rating of AAC,etc.are analyzed when the passive circulating current and active circulating currents(compensation circulating current)are synthesized into a composite circulating current with different ratios in the AT-IPR.The optimal circulating current proportioning parameters(the tap turns ratio of AT-IPR and the compensation circulating current form)are designed with the objective of minimizing the output voltage ripple.The voltage and current ratings and capacities of the rectifier elements are calculated,and the power losses of rectifier are evaluated.The theoretical analysis shows that the method requires only a low-capacity AT-IPR with series AAC to significantly suppress the input current harmonics and output voltage ripple of the rectifier.Taking a 12 k W rectifier system as an example,the performance of active,passive and hybrid harmonic suppression rectifiers are compared under the same parameter conditions,and the advantages of the hybrid harmonic suppression method in terms of AC and DC-side power quality as well as harmonic suppression cost are clarified.The results of the case study show that the hybrid harmonic suppression achieves better input and output power quality of the rectifier with relatively less increase in the k VA rating of the magnetic device and additional losses.Finally,the validity and correctness of the theoretical analysis is verified by simulation experiments. |
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