AC Fault Analysis on NPC based Multi-terminal Hybrid AC-DC system

This paper deals with the interconnection of three AC systems via High voltage DC links. Both synchronous and asynchronous connections of the AC systems are considered. Neutral point diode clamped (NPC) based VSC HVDC system is considered for analysis. NPC based VSC HVDC provides three level DC voltages as VDC / 2, - VDC / 2 and 0. It reduce total switches connected in series. Due to this, harmonics are also reduced comparatively to two level converters. DC voltage and reactive power control mode is selected for both inverters. Real and imaginary power flows are controlled at rectifier end. The interconnected system is analyzed under three phase fault. The AC faults occurs at the end of inverter-1 (connected to AC system-2). The behavior of AC currents, AC voltages, active and reactive powers and DC voltages are studied in case of AC faults. All results are performed in MATLAB Simulink environment.