Alternate arm modular multilevel converter for HVDC systems

The Modular Multilevel Converter (MMC) and Alternate Arm Modular Multilevel Converter are the emerging converter topologies which are most effective and suitable for HVDC systems. The AAMMC represents a hybrid multilevel converter topology with high capability for high voltage applications. One of the serious problems of the HVDC system is the blocking of DC side faults. The MMC can be used to limit the DC side fault current but the main disadvantage this converter it requires double number of submodules to switch in reverse voltage and has inability to produce negative voltage due to half bridge submodules. This paper represents the schematic and working principle of AAMMC which can be used to block the DC side faults. The control and modulation schemes are used for converter operation and shows better advantages for balancing the capacitor voltage across all submodules. The decoupled current control technique is used for DC link voltage control, active and reactive power control. Thus the converter provides the advantages such as lower number of submodules as compared to MMC which helps to minimize the size and volume of the converter station, DC fault tolerance property and generation of almost sinusoidal multistep harmonic free AC voltage. The simulation results for fault tolerant 21 level AAMMC are discussed and analyzed for active-reactive power control and DC link voltage control to demonstrate the effectiveness of the implemented system.