HAO Liangliang,ZHAN Qingqing,CHEN Zhengguang,et al.Analysis of DC current transient process under AC system fault at LCC-MMC hybrid HVDC sending end[J].Electric Power Automation Equipment,2019,39(09):220-227.
HAO Liangliang,ZHAN Qingqing,CHEN Zhengguang,et al.Analysis of DC current transient process under AC system fault at LCC-MMC hybrid HVDC sending end[J].Electric Power Automation Equipment,2019,39(09):220-227.DOI: 10.16081/j.epae.201909050.
Analysis of DC current transient process under AC system fault at LCC-MMC hybrid HVDC sending end
LCC-MMC(Line Commutated Converter-Modular Multilevel Converter) hybrid HVDC transmission solves the problem of commutation failure at traditional DC receiving end. At present,the project demonstration of receiving end flexibility in Gezhouba-Shanghai HVDC system has been carried out,and the focus is on the problem of fault ride-through problem which causes rapid decrease of DC current under the AC fault at the sending end. Therefore,firstly,the Laplace arithmetic circuit is obtained according to the system equivalent circuit of the AC fault at the sending end. Based on the loop current method,the transient process of DC current is obtained by Laplace inverse transformation,and the attenuation and oscillation components of the transient current are analyzed. The electromagnetic transient simulation model of Gezhouba-Shanghai HVDC system is established in PSCAD/EMTDC,and simulative results verify the correctness of analysis. Furthermore,the approximate analytical expressions of DC current and its zero-crossing time are obtained by neglecting the oscillation component of transient current. Finally,the influence of AC voltage dropping degree,smoothing reactor and control strategy on DC current zero-crossing time is analyzed by analytic expression. The proposed method can provide the basis for protection value setting of sending end AC system and the selection of smoothing reactor parameters in LCC-MMC hybrid HVDC system.
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