Analysis Of Reactive Power Balance Characteristics Of LCL-HVDC

In order to solve the problems of traditional LCL-HVDC,such as the Converter transformer,inverter side commutation failure,serious noise pollution harmonic harness and reactive power balance,such as large transformer harmonic loss,proposed an LCL-HVDC project group,in order to make the new dc transmission technology to engineering application,also need to study a series of theory and technology.In this paper,only the reactive power balance characteristics of LCL-HVDC are studied.Compared with the LCC converter principle,the LCL converter eliminates the filter and reactive compensation capacitor on the AC side,and the capacitor C is paralleled in the valve side winding of the converter transformer,and then the current limiting inductor L is connected in series.Among them,the current limiting inductor L limits the di/dt value of the converter valve,and the shunt capacitor C can provide DC voltage and commutating voltage,and perform reactive power compensation to suppress harmonics.The ideal capacitance value should meet the harmonic limit of the AC bus and the low reactive power exchange with the AC system.This paper mainly includes the following work:Firstly,the structure of the HVDC transmission system and the reactive power characteristics of the converter station are analyzed,the topological structure of LCC and LCL converter is studied,the working principle is analyzed,the mathematical model of the converter and the simplified model of the corresponding HVDC system are established,and the reactive power characteristics of the system are studied,and the corresponding steady-state equation is derived.Based on the LCC-HVDC control strategy,the control mode of the LCL-HVDC system studied in this paper was determined,and the overall framework of the LCL-HVDC control system was built.Taking the Jiuquan-Hunan ±800k V HVDC transmission project as an example,the reactive power balance and configuration of LCC-HVDC are studied.Secondly,the reactive power balance and reactive power control strategy are studied,and the reactive power balance and configuration of LCL-HVDC are analyzed.The parameters of the main loop of the LCL-HVDC system were determined by referring to the parameters of the CIGre standard model,and the values of current limiting inductance and shunt capacitance suitable for the system were selected.The reactive power balance of the LCL-HVDC system was analyzed,and the configuration and grouping of reactive power compensation devices under rated power and reduced power operating conditions were carried out respectively.Finally,based on the CIGRE standard model LCL-HVDC control system and reactive power configuration scheme,using MATLAB to build the CIGRE standard model based on the LCC-HVDC and LCL-HVDC simulation models,respectively,the LCL-HVDC under the rated power operation and power down operation two ways to run.The switching process of reactive power device is analyzed and the configuration scheme of reactive power device is verified.The power factor,harmonic distortion rate and voltage and current fluctuation rate of LCC-HVDC and LCL-HVDC systems are compared and analyzed,and the feasibility of the design of LCL-HVDC system and reactive power configuration scheme is verified.