A Vector Voltage Modulator for a Dual Inverter with a Floating Bridge to Operate in Normal and Fault Tolerant Mode

The dual inverter multilevel converter is characterized by a elementary structure using two well-known three-phase bridge inverters supplied by two independent DC sources. However, it can be supplied only by a single DC source if one of the bridges uses just a floating DC capacitor. In this case the control is more complex since it is also required to ensure the capacitor voltage regulation. Besides this, if a fault in one of the switches is also considered, the operation of the converter in fault operation mode becomes even more complex. This paper presents a vector voltage modulator that in addition to track the reference of the output AC voltages, also allows the capacitor voltage regulation of the floating bridge. The capability of this modulator to function properly the converter in fault tolerant mode under an inverter open switch will also be analyzed. This analysis will allow to verify that the proposed control and modulation strategy presents inherent fault tolerant capability to open switch fault, since it does not require any fault detection algorithm or change in the control or modulation strategy. The capability and operation of the proposed vector voltage modulator will be verified through several simulation studies