Research On The Method Of Wideband Measurement And Circuit Modeling Of High Voltage DC Thyristor Modules

High Voltage Direct Current (HVDC) systems play an important role in the long transmission, bulk power and the link between two ac power systems stability. Currently, HVDC transmission projects with800kV level have been built-up in China and its first1100kV transmission line has also been planned. Due to the progress and its excellent performance, HVDC transmission projects will be an important part of the grid in the future in China. The thyristor valve operates in a3-phase bridge circuit, where it will be exposed to impulse and switching overvoltage originating in the ac and dc systems. The magnitude and waveform of the overvoltage which appear across the valve should be taken into consideration because it will lead to the power safety and reliability as well as the rational design of thyristor valves, converter transformers, smoothing reactors and so on. What’s more, there is a quite severe electromagnetic interference level near the valves which is due to the high power transient processes caused by the rapid changes in the valve voltage at the ignition or turning-off moments. Such above phenomena can cause harmful interference to open-wire carrier system and secondary equipment in converter. Therefore, it is necessary to built wideband modeling of thyristor module to predict the electromagnetic environment and calculate overvoltage distribution of valve modules to make effective measures.This thesis is aimed at the methods of wideband measurement and circuit modeling of1100kV thyristor modules. The main contents are as follows:(1) The operating theory and key functions of Impedance Analyzer are discussed and the impact factors of leads are presented according to the measurement results. On the basis of that, impedance of the equipment in1100kV thyristor module is measured by such above method.(2) A wideband measurement method based on high voltage pulse is presented. Theoretical analysis, numerical simulation and experimental methods are used to verify the effectiveness of the measurement method. The measurement method can be applied to the high frequency measurement of large size equipment in the power system.(3) An efficient method is proposed to construct equivalent circuit model from frequency response with guaranteed physical meaning of equipment. The basic idea of the proposed method is to represent the equivalent circuit according to the characteristic of equipment. Genetic algorithm is then applied to find the values by minimizing the errors between the desired frequency response and that produced by the equivalent circuit. Since the equivalent circuit consists of only passive elements, the circuit physical meaning is always guaranteed.(4) Transient voltage experiments are carried out and the voltage distributions in1100kV thyristor module are measured. The validity of the equivalent circuit of valve module is verified according to the measured results and calculated results.