Research And Application Of Wideband Circuit Modeling Method Of Converter Systems In Converter Stations

Wideband modeling of converter systems is essential to predict the electromagnetic environment and calculate overvoltage distributions of thyristor valves in High Voltage Direct Current (HVDC) converter stations. This tenology is also the basic equirement of the national independent innovation of electromagnetic compatibility (EMC) in HVDC converter stations in China. Supported by the National Natural Science Foundation of China (Grant No.50707008) and the Eleventh Five-Year Plan for National Science and Technology (Grant No.2006BAA02A20), the modeling methodology of wideband equivalent topology of converter systems in HVDC converter stations is proposed to calculate the overvoltage distributions in the thyristor valves and to predict the electromagnetic environment of±800kV converter station. Compared with the measured results, the proposed methods are proved to be efficient. The main innovative achievements are as follows:1. An efficient method is proposed to model the passive devices with traditional equivalent circuit combined with black-box theory. The new method enables the designers to retain their existing physical models while providing a means to capture the high frequency effects accurately. Based on this method, wideband equivalent circuits of the valve components, such as thyristor, saturable reactor and snubber circuits, are obtained based on impedance measurement.2. Stray capacitances and inductance of different type of thyristor valves are extracted and analyzed. Combined with the wideband models of valve components, wideband model of the whole valve system is presented. The wideband models of the key equipments in AC and DC yard are also proposed in this paper, such as converter transformer, smoothing reactor, filters, et al.3. Overvoltage testing expriments are carried out. Voltage distributions are measured both in valve modules and valve tower. The experimental results verify the validity of the proposed wideband model of thyristor valves. Electromagnetic disturbances are measured on site and the results indicate that the wideband topology of the whole converter systems is effective.4. Based on the wideband equivalent circuit of the thyristor valves, the voltage gradient of valve layers and voltage distribution among valve components were calculated under different kinds of overvoltages including switching, lightening and fast front overvoltage, and the influence factors were also discussed. Some regularity was obtained, e.g. the stray capacitances of the valves have an effect on the overvoltage distribution among valve components, while the parameters of the valve components can influence the voltage drop on thyristors. Lastly, some improved measures are proposed.5. Based on the wideband topology of the whole converter systems, the characteristic of the conductive electromagnetic disturbances in±800kV HVDC converter station is simulated and anslyzed. And the radio interference level is also calculated both inside and surrounding the converter station. These results could have a guide on immunity and valve hall screening design of future HVDC converter stations in China.