There are various challenges associate with multilevel converters, such as reduction of the number of devices, appropriate modulation scheme, loss management, fault tolerance operation, control method, capacitor voltage balancing and pre-charging. In flying capacitor-based multilevel structures, a main challenge is precharging of dc capacitors during the converter startup. The pre-charging of dc capacitors is required to eliminate the high overvoltage across the semiconductor devices and limit the high inrush current. In this thesis, appropriate methods for pre-charging of dc capacitors in flying capacitor-based multilevel structures is studied. In this regard, appropriate methods for startup of FCM, 5L-ANPC, C and 4L-HC converters are proposed. The startup of FCM converters is studied based on modulation schemes and their operation modes. The startup procedures of the other mentioned multilevel converters are investigated using various methods in rectification and inversion modes. The operation of these methods is studied for different applications. In the 5L-ANPC and 4L-HC converters, the DC link is divided to several parts. As a result, the startup procedures of these converters in inversion operating mode are more simple than other converters. In rectification operating mode, the startup procedure is implemented by FCS-MPC method. The simulations in the PSIM software are provided for proposed startup procedures. In order to verify the practicability of the proposed startup method of the 4L-HC converter, a scaled-down prototype is implemented and the associated results are presented. Keywords : Startup procedure, Multilevel converter, Flying capacitor, MPC method.
