Comprehensive Factors Analysis And Detection For DC Short Circuit Faults Of MMC-HVDC Grid Based On Transient Energy

Modular multilevel converter based high voltage direct current grid is one of the key technologies for the large-scale transmission of new energy and the future energy internet.The research of the protection technology for the dc short circuit fault in MMC-HVDC grid is not perfect at present,and further research is needed in the aspects of the failure mechanism,comprehensive analysis of the influencing factors and comprehensive optimization of the parameters.This paper mainly researches on the transient energy characteristics and the comprehensive analysis of the influencing factors of dc short circuit fault in the MMC-HVDC grid,and based on the analysis conclusion a fault detection method is proposed.The main research contents are as follows:(1)The electromagnetic transient simulation model of MMC-HVDC grid is constructed on PSCAD.Based on the transient energy flow method,the temporal and spatial distribution characteristics of transient energy flow in the system under the condition of dc short circuit fault are analyzed,and the difference between different dc line fault such as dc line broken and lightning are compared,which can provide theoretical bases for the dc short circuit fault detection.(2)To deal with the difficulty exists in the comprehensive analysis and optimization of multiple influencing factors for the dc short circuit fault in MMC-HVDC grid,a solution based on the central composite experiment design is proposed,which is by obtaining quadratic regression model by the central composite experiment design and electromagnetic transient simulation data,setting the transient energy flow as the response variable and using the statistical analysis method to carry out the comprehensive analysis and evaluation of the influence degree of multiple influencing factors,and comprehensive optimization for the multiple influencing factors is implemented based on the quadratic regression model.The simulation experiments verify the effectiveness of this comprehensive optimization method.(3)Based on the energy storage of current limiting reactors and capacitors,storage state vector of MMC and the detection criterion of dc short circuit fault,including the startup criterion,fault line judgement criterion,fault zone criterion as well as interference elimination criterion are constructed.Using the four-terminal dc ring gird PSCAD simulation model,the simulation of lightning,dc line broken and short circuit faults with high impedance are carried out respectively.The simulation results show that comparing with other fault detection methods,this method has simpler detection mechanism,lower detection frequency and better anti-interference.