A new calculation method for fault transient expression of ring DC systems

When the fault occurs in the ring DC system, the fault process can be divided into the current discharge stage, the diode freewheeling stage and the steady-state phase under the AC power supply. This paper mainly studies the capacitor discharge stage. Firstly, the multi-terminal DC system is decomposed into n single-ended systems. Secondly, write the state equation of the single-ended system and solve the expression of fault current and voltage. Thirdly, get the fault analysis expression of the multi-terminal system by the relationship expressions for each transient value between single-ended system and multi-terminal system. The simulation are carried out by MATLAB / Simulink to provide the basis for fault location and isolation.