Research On Harmonic Suppression Of Series Isolated Multi-Pulse Rectifiers Based On DC Side Harmonic Injection Method

Series multi-pulse rectifier is widely utilized in aerospace,electric vehicle charging,wind power grid connection,and other high-power rectification applications as the interface between AC power grid and power equipment.However,the large number of strong nonlinear components and magnetic devices used by the rectifier will cause significant harmonic pollution and electromagnetic interference to the utility grid.This work investigates the harmonic suppression performance of a series isolated 12-pulse rectifier with the DC side single passive injection,dual passive injection,and hybrid injection approaches respectively,with the goal of enhancing the power quality and robustness of series multi-pulse rectification systems.The specific contents are as follows:(1)Equivalent modeling is used to resolve the relationship between the characteristic electric parameters of the fundamental 12-pulse rectifier at AC and DC side.The winding turns ratio of an isolated zigzag phase shifting transformer is determined using the multi-pulse rectification operating theory.The mathematical expression of the input voltage at AC side is obtained by combining the rectifier’s operating mode,taking into account the three-phase balanced input and the constant voltage load at DC side.The simulation and experimental results demonstrate that the current harmonic distortion at AC side of the series 12-pulse rectifier is less than the voltage harmonic distortion as a result of the influence of the source side inductances,but it still does not meet the pertinent harmonic standards.(2)To reduce the harmonics of basic series 12-pulse rectifier system,a series 24-pulse rectifier with DC side single passive voltage harmonic injection circuit is studied.The working principle of the 24-pulse rectifier is analyzed.The realization process of input voltage step waves from 12 to 24 is analyzed.The expression of 24-step wave values of AC input voltage is derived.The optimal turn ratio of the single-phase injection transformer is designed to reduce the harmonic distortion of AC side voltage as far as possible.The magnetic device capacity of the rectifier is calculated.According to simulation and experiment results,the series 24-pulse rectifier based on the DC side single passive harmonic injection method has the advantages of leakage balance,a simple structure,and strong robustness.The VA rating of the injection transformer only accounts for 2.04% of the output power,and the cost of harmonic suppression is low,but the effect of harmonic suppression needs to be improved.(3)To further reduce the harmonic content of the series 12-pulse rectifier,a series36-pulse rectifier with dual passive harmonic injection circuits at DC side is studied.The working modes of the rectifier are determined by combining the structure of the auxiliary dual passive harmonic injection circuits.The realization process of the input voltage step waves from 12 to 36 is analyzed.The expression of 36-step wave values of AC input voltage is derived.The optimal turn ratios of two single-phase injection transformers corresponding to the current harmonic injection circuit and the voltage harmonic injection circuit at DC side are designed.The harmonic properties of the voltage and current both AC and DC side in the rectification system are examined in conjunction with the mathematical analytic formulas.The fault tolerance of the rectifier is analyzed when the diode in the auxiliary passive circuits is open.The simulation and experimental results show that the series 36-pulse rectifier based on the DC side double passive harmonic injection method has the advantages of strong harmonic suppression ability and robustness,but the auxiliary circuit uses two single-phase injection transformers,which also increases the volume and cost of the rectifier.(4)To improve the device utilization rate and harmonic suppression ability of series12-pulse rectifier,a series 36-pulse rectifier with DC hybrid voltage harmonic injection circuit is studied by integrating the advantages of DC passive and active harmonic injection technology.The DC hybrid voltage harmonic injection circuit is designed.The working principle of the rectifier is analyzed.Combined with the working modes of the rectifier,the realization process of the input voltage step waves from 12 to 36 is analyzed.The expression of 36-step wave values of AC input voltage is derived.The optimal turn ratio of the single-phase injection transformer,IGBT on-angle and its control circuit are designed.The voltage and current characteristics of the rectifier are analyzed.The switch loss is calculated.The operation features of the rectifier under normal conditions and IGBT fault are investigated in light of the high failure rate.The simulation and experimental results show that the series 36-pulse rectifier based on the DC side hybrid voltage harmonic injection method has high utilization rate,simple structure,low harmonic content.Under an IGBT short circuit fault,the auxiliary harmonic circuit fails,but the rectifier maintains its strong robustness and high output voltage gain properties,allowing it to be used in high voltage and high power converter applications.