| Due to the adverse distribution of energy and load in China,energy development gradually moves towards the west and north.However,the core electricity load is in the eastern part of economic development.In order to balance the supply and demand of electricity,the UHVDC transmission emerges has developed rapidly to make sure electrical could meet the needs of economic in China.Nevertheless,the side effects of harmonics have affected the normal electrical equipment operating.Besides,network loss increased.Moreover,the security,reliability and stability of network also reduced.The background of this assignment is the AC side system of UHVDC converter station in the particular area.The author will further analysis the background harmonic of converter station and the influences between harmonic of converter station and the harmonic of AC side network.According to the data collected which showed the regional power grid converter placement of near zone and the power grid map based on geographical structure in 2016,to build a simplified equivalent simulation model of AC power grid in ETAP 2016.It is to ensure the reliability of the simulation model and the data of UHVDC converterstation AC power grid.What's more,the author will analysis the harmonic power flow and compare the simulation value and measured value,to make sure that the model is reasonable and accurate,which can be used as theoretical support and basic platform in our research.Moreover,a model equivalent method in 2016 was applied to the simulation model of the AC side power grid of UHVDC converter station in 2019 in the particular area,and the input data was determined with the annual growth rate of load.In the 2019 simulation model,there are two different operating modes,DC overhaul and bipolar full voltage.They are used for DC transmission lines.And in each way,the harmonic analysis is carried out in four different working conditions.The harmonic characteristics of the two modes are analyzed,and the background harmonics are provided for the converter station in the mode of DC maintenance and operation;The theory of characteristic harmonics in converter station is verified under the bipolar full voltage operation mode.The simulation results show that the DC transmission has serious influence on the harmonic of the AC side network.In the end of this assignment,the structure and working principle of the AC filter circuit are analyzed.According to the harmonic characteristics,the AC filter scheme is designed under the condition of small start-up and large load operation.After the filter is installed,the harmonic analysis of the AC power grid is compared with the original harmonic data to verify the rationality of the design parameters and the scheme of the filter.When the DC bipolar full pressure is running normally,the AC power filter bank cannot control the harmonics which generated by UHVDC converter station.The harmonic condition will be compared and analyzed before and after the AC bus added the filter.The simulation results show that the designed filter scheme can play a good role in restraining the harmonics of the HVDC transmission system.It is providing a theoretical reference for the converter station to install filters. |
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