Analytical Calculation and Analysis Methods of DC Overcurrent During Commutation Failure Applicable for Voltage Stability Analysis of Sending End System
During commutation failure,the DC current rises substantially,causing a large amount of reactive power consumption,which endangers the safety of equipment and the voltage stability of the sending-end system.Considering the insufficient attention to overcurrent during commutation failure,this paper establishes an electromechanical transient overcurrent model applicable for voltage stability analysis of the sending end system and then reports upon some research results from the perspective of influence factors and fast calculation.First,the paper points out that the measuring module of VDCOL cannot be ignored in the quantitative calculation.Then,an approximate linear relationship between the commutation bus voltage and the DC current is deduced,and an algebraically decoupled second-order model for analyzing the overcurrent is established with the singular perturbation method.Based on the trapezoidal integral rule,a fast estimation method for the peak value of overcurrent is proposed.Combined with the phase diagram,the influence of control parameters and grid structure on the overcurrent and low voltage are analyzed.Finally,the voltage instability problem of losing solution caused by overcurrent is preliminarily explored.The analysis results and fast estimation method are verified by numerical examples.
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