The Research On Operation And Electromagnetic Characteristics Of Integrated Multi-winding Inductive Filtering Converter Transformer

In the field of AC and DC power conversion,harmonic suppression and reactive power compensation have being occupied an important position.The traditional passive LC branches,which are usually installed at the primary side transformer,can relieve the bad influence of harmonics on public grid.The adverse influence on the transformers,such as power losses,vibration and noise,however,cannot be suppressed.Inductive filtering technology is a kind of new harmonic suppression method,which is based on harmonic flux suppression mechanism in transformer.By blocking the valve side harmonics and reactive power currents from passing through transformer,the adverse influence on transformer caused by those components are totally eliminated.In this paper,the operation characteristic of the inductive filtering rectifier transformer and its filtering system,which is applied to an industrial rectifier system,is analyzed first.And then,an integrated multi-winding inductive filtering converter transformer with novel topology and its filtering system are proposed.As for study of the operation and electromagnetic characteristics,the following aspects are included:(1)The working mechanism and implementation requirements of inductive filtering technology is analyzed,concentrating on the operation characteristic of the inductive filtering rectifier transformer and its filtering system,which is applied to an industrial rectifier system.And then,the mathematical model of this system is built,and current relationships between the primary winding side and two secondary winding sides are derived.Based on those relationships,the harmonic suppression mechanism and reactive power compensation characteristic are fully studied.Simulation and experimental results show that the performance of this new rectifier system on harmonic suppressing and reactive power compensating is excellent.The harmonic content on the primary side currents is significantly reduced.By changing the transforming path of harmonics and reactive power currents,the power losses caused by those components are decreased,the system efficiency is enhanced,and the goals of energy saving are achieved.(2)An integrated multi-winding inductive filtering converter transformer and its filtering system applied to the HVDC conversion station are proposed and the corresponding operation characteristics are studied.The mathematical model of inductive filtering transformer with two paralleled-connected delta filter windings and its filter system are established.The current relationships between different windings are derived,and the harmonic current paths and reactive power compensation characteristics of this new system are demonstrated.The simulation and experimental results show that the(12k-5)th and(12k-7)th(k(28)1,2,3,(43))harmonics can be effectively suppressed with no corresponding filtering branches if the two delta windings designed with zero impedance are parallel-connected.The 11 th and 13 th tuned filtering branches installed at the taps can achieve the desired filtering performance.Flowing in the superconductivity closed-loop provided by the two delta windings,3nd harmonic current cannot be transformed to the primary side.(3)The field-circuit coupled model of the integrated multi-winding inductive filtering converter transformer and its filter system is established.Based on that model,some characteristics of the inductive filtering converter transformer,including the electric field characteristic,magnetic field characteristic,windings' electromagnetic force characteristic and the power losses characteristic of windings core,are analyzed.It can be observed that the implementation of inductive filtering can suppress the harmonic magnetic potential,improve the internal electromagnetic environment of the transformer core,and fully exploit the transformer's internal electromagnetic potential.The damages of transformer cause by harmonics,such as power losses,vibration,and noise,can be improved fundamentally.(4)The mechanism of DC bias of converter transformer is analyzed.And the bi-direction harmonic suppression mechanism of the integrated multi-winding inductive filtering converter transformer under the condition of DC biasis studied.Considering core saturation effect of the inductive filtering converter transformer,the model of DC bias is built,and the transformer's harmonic distribution characteristics are also analyzed.Beside,to study the electromagnetic characteristics of the DC magnetic bias,the field circuit coupling model of the inductive filtering converter transformer under DC magnetic bias is built.The corresponding simulation results show that the distributions of all windings leakage magnetic field are greatly improved,together with a significant reduction on windings' electromagnetic force,which is good for cutting the vibration and noise pollution of converter transformer down under DC bias conditions.(5)By using the ANSYS software,the finite element simulation model of the integrated multi winding inductive filtering converter transformer is established and the winding vibration modal analysis is implemented.The analyzed results show that resonances on fundamental or harmonic orders cannot be excited if the structure of transformer winding is properly designed.Based on the electromagnetic force results obtained above,a simulation study on the vibration characteristics of the inductive filtering converter transformer is finished,with a method combined with the transient dynamics and finite element analysis.As shown by the simulation results,the internal electromagnetic environment of the transformer ismuch improved,leading to a reduction on the vibration of windings.