Broadband Modeling Method Of Converter Transformer

As one of the core equipment in the HVDC transmission project,the converter transformer is the key to connecting the AC system and the converter.The operating environment of the converter transformer is harsh,its operating voltag e and current spectrum are complex,and it is frequently affected by transient disturbance and DC bias.In order to avoid the harmonic resonance of the system and monitor the running state of the transformer,it is necessary to fully grasp and understand t he equivalent modeling method of the converter transformer and obtain the variation law of its equivalent impedance.Therefore,it is necessary to study the broadband model of the converter transformer.In this context,the paper has done the following res earch work:(1)This paper summarizes the work of the predecessors,and summarizes the mainstream transformer modeling methods and distribution parameter calculation methods.Then the factors that need to be considered in the broadband modeling process and the principles of their generation are analyzed in detail,and the importance of various frequency-varying factors in different frequency segments is described.(2)Combining the inductance characterization model and the capacitance characterization model of the transformer,the classical wide frequency domain model of the converter transformer is obtained.As the distribution parameters and spurious parameters of the transformer increase with frequency,the distribution becomes more obvious.A segmented wide frequency domain modeling method for converter transformer is proposed.The model segments the transformer for the frequency segment studied.The primary side winding and the secondary side winding of the converter transformer are respectively divided into several identical units according to their structure and number of segments,and the electromagnetic characteristics of the transformer capacitance effect are considered in the modeling process.Then based on the physical size and electrical parameters of the converter transformer,a three-dimensional finite element simulation model of the converter transformer is established in Maxwell 3D simulation software,and the coupling inductance and coupling capacitance between the primary winding and the seco ndary winding of the converter transformer are The capacitance to ground was calculated and the resistance parameter was finally calculated.(3)This paper uses HIOKI IM3570 impedance tester to measure the converter transformer,and measures the impedance value of the valve side winding when the converter transformer is short-circuited to the grid side.The equivalent circuit model of the different number of segments of the converter transformer is built in the PSCAD software.The simulation results show that the segmentation model can more closely reflect the characteristics of the converter transformer generating multiple resonance points at high frequency,which is more suitable for complex Circuit simulation calculation and fault analysis under working conditions.Then,in order to reduce the quality factor of the resonance of the model,a fixed resistor is connected in series with the branch where the stray capacitance is located.The simulation results are compared with the measured data,and the segmented wide frequency domain model of the converter transformer is found within the allowable error range.It can well reflect its impedance characteristics.In this paper,the research on wideband modeling method of converter transformer is carried out.In t he frequency range of power frequency to one megahertz,the established model can simulate the impedance characteristics of transformer well,and it has certain guidance for the optimization design of converter transformer.significance.(4)By changing the capacitance parameters and inductance parameters in the transformer wide-band segmentation model,the influence of parameter variation on its frequency response curve is analyzed,and then the transformer broadband is used to simulate the radial deformation,axial deformation and daytime of the transformer winding.Short-circuit three faults with high frequency of occurrence,summarizing the trend of the frequency response curve of the three transformers after different faults in different frequency bands.