Short-circuit Calculation Method of Whole Network Characteristic Quantity During the Whole Fault Process in Complex Multi-terminal Flexible DC Distribution Network
Multi-terminal flexible DC distribution network has small short-circuit damping and low inertia,and the fault development presents the characteristics of strong nonlinearity and stage due to the existance of a large number of power electronic devices in the system.Conventional short-circuit calculation methods concern fault characteristics of"points"and"lines",making it difficult to consider the network-level characteristics.Therefore,this paper focuses on the whole process of short-circuit fault from capacitor discharge to AC-side feed current,and introduces the theory of DC fault ports.On this basis,the fault network is simplified by using high-frequency equivalent characteristics,and then the approximate solution of the fault current in the capacitor discharge stage is obtained by the Laplace inverse transformation.Subse-quently,the characteristic quantity of the whole network is obtained by fault-port impedance.In the steady-state AC feed stage,the converter port transfer matrix is established,the series-connected nodes in the network are eliminated after commutation overlap correction,and then the steady-state short-circuit calculation method suitable for multi-terminal flexible DC power grids is obtained.Finally,a simulation model is built based on PSCAD/EMTDC platform,which veri-fies the accuracy of the proposed short circuit calculation method under different fault locations and fault resistances.
multi-terminal flexible DC distribution networkshort circuit calculationfault porthigh-frequency equiva-lencecommutation overlap
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