Research On Radiated Disturbance Induced By Modular Multilevel Converter

Modular multilevel converter based high voltage direct current(MMC-HVDC)technology is developing rapidly.As one of the core equipment of converter station,the design and manufacture level of converter valve determines the development of the voltage source converter based high voltage direct current(VSC-HVDC)technology to a certain extent.The electromagnetic disturbance level of converter valve is also an aspect that must be considered in the design of valve tower and valve hall.The MMC valve includes dozens or even hundreds of sub-modules,each sub-module has at least two IGBTs inside.IGBT will produce rapid changes in voltage and current during on-off process,and will also produce radiated electromagnetic disturbance.High-frequency voltage and current propagate through the main circuit of sub-module and converter valve and stray capacitance,which eventually leads to radiated electromagnetic disturbance of converter valve.In order to obtain the radiated electromagnetic disturbance characteristics of IGBT switching process,an IGBT module experimental system is built in a shielded anechoic chamber to study IGBT’s electromagnetic disturbance.The system includes the IGBT,the control drive circuit,the electromagnetic shielding box and other equipment required for IGBT to work normally.According to the structure and material of IGBT module,a fine calculation model to calculate the IGBT radiated electric field is established,and the influence of stray parameters of IGBT is considered.The experimental measurement results are used to verify the effectiveness of the modeling method.Finally,through calculation and measurement,the influencing factors of IGBT radiated electromagnetic disturbance are analyzed.Based on the sub-module used in practical engineering,the radiation electromagnetic disturbance calculation model of the sub-module is established by using IGBT radiation electromagnetic disturbance modeling method,the voltage and current characteristics of the sub-module port are measured,and the distribution characteristics of radiation electric fields inside and outside the sub-module are calculated by using the method of moments.The influence of stray capacitance between sub-module shells,stray capacitance between shell and copper bar,and stray capacitance of copper bar to ground are analyzed,and the calculation model of radiated electromagnetic disturbance of sub-module group suitable for engineering is established.Finally,from the perspective of improving the level of electromagnetic compatibility,the paper puts forward suggestions on the layout of sub-module internal control circuit board.A ±320kV MMC-HVDC station,a ±200 kV five-terminal MMC-HVDC station and a ±420kV back-to-back MMC-HVDC station are selected to measure the electric field intensity inside and outside the converter valve hall during its stable operation according to relevant measurement standards.The electric field characteristics of different positions in the MMC-HVDC station are obtained,and the attenuation characteristics of electromagnetic disturbance intensity changing with distance in the converter station are analyzed.The calculation model of MMC-HVDC converter valve is established to calculate the radiated electromagnetic disturbance.The radiated electric field intensity of a ±500kV MMC-HVDC converter station is predicted,and the shielding effectiveness of valve hall is calculated.In this paper,the radiated electromagnetic disturbance characteristics of modular multilevel converter are studied by combining electric field measurement and modeling calculation.The radiation electric field modeling and calculation method at IGBT level is applied to sub-module level,and the influence of stray parameters among sub-modules is analyzed,thus establishing a radiation electromagnetic disturbance calculation model for sub-module groups suitable for engineering.The sub-module modeling method and excitation source characteristics are applied to the converter valve model,and an engineering applicable converter valve radiated electromagnetic disturbance calculation model is established.Research on radiated electromagnetic disturbance characteristics of modular multilevel converters can provide suggestions for improving electromagnetic compatibility level of converter equipment and electromagnetic shielding design of converter stations,and is of great significance to MMC-HVDC projects to be built in China now and in the future.