The Research On The High Frequency Characteristice Of The ±1100 KV Converter Station

During the operation of the UHVDC project,high-frequency harmonic noise is generated due to the rapid opening or closing of the converter valve,and transmitted to the AC side and the DC side respectively through the conduction channel.The harmonics in the 30 kHz-500 kHz band may interfere with the power carrier communication(PLC)and affect its normal communication.Therefore,it is necessary to measure the high frequency noise of the converter station of the UHVDC project and determine whether it is necessary.In this paper,the basic principle of high-frequency noise generated by commutation valve is deeply analyzed and the high-frequency noise level is studied in detail with the actual structure of ±1100 kV UHVDC transmission project:(1)The mechanism of PLC noise generation is studied,and three high-frequency models of the converter valve are proposed according to the actual structure.The high-frequency noise levels generated by the similarly designed HVDC engineering converter valve group are compared.Determine a converter valve equivalent model to reflect its actual high-frequency characteristics;thereafter,use the PSCAD simulation platform to build a model of the Zhundong-Weinan UHVDC transmission project,and obtain the commutation station and inverter station commutation through simulation calculation.The voltage waveform before the smoothing reactor is set,and the high frequency noise level of the transient process is obtained by Fourier transform.Considering the complexity of the high-frequency model of the converter valve,this paper proposes to express its spectral characteristics according to the measured noise level,and further proposes a partial pressure model according to the distribution of the internal voltage of the converter,and obtains the noise represented by the formula.The subsequent study of the source partial pressure model as an excitation source for the high-frequency characteristics of the converter station is more realistic.The influencing factors of the noise level are further studied,and the high-frequency noise level of the relevant measurement points is determined under different trigger angles and transmission powers.When the trigger angle is larger,the transmission power is larger,and high-frequency noise level is larger.(2)Researched a series of high-frequency models of converter station equipment,including converter valves,converter transformers,smoothing reactors,transmission’--/lines,wall bushings and other key equipment.For the converter valve,based on the actual circuit structure,this paper analyzes the stray parameters existing between the components,and builds a detailed high-frequency model of the converter valve according to the physical structure of the±1100 kV converter valve.For the converter transformer,two high-frequency models are studied respectively.According to the inter-winding capacitance of the converter transformer and the capacitance of the low-voltage winding,a commutation transient model with integrated leakage inductance and distributed capacitance is proposed.Its accuracy is 30 kHz-100 kHz;according to the actual winding structure unit of UHVDC converter transformer,the converter transformer modeling method suitable for UHVDC engineering is proposed.The obtained noise level is basically consistent with the reference spectrum,considering the change.The actual structure of the flow transformer and the ease of calculation,this paper determines the commutation transient model with integrated leakage inductance and distributed capacitance as its high frequency model.For the smoothing reactor,the high-frequency modeling method of this paper is similar to the converter valve.Firstly,its working principle is studied.Secondly,the existing spurious parameters are determined according to the actual physical structure,and the completed flat wave is obtained through parameter collection and calculation.Reactor high frequency model.(3)The design principle of PLC high-frequency filter is studied.According to the complete high-frequency noise conduction channel of DC system,the high-frequency noise level of relevant measurement points is calculated.Compared with the international standard high-frequency noise limit,whether the requirements of the high frequency limit are met.Obtain the high frequency noise amplitude that needs to be reduced,and then build the corresponding high frequency filter type,and optimize the parameters of the tuning device to achieve the purpose of reducing the construction cost.