The demands of power electronics with high power capability have increased in the last decades. These needs have driven the expansion of existing power electronics topologies and developing new power electronics generations. Multilevel inverters (MLI) are one of the most promising power electronics circuits that have been implemented and commercialized in high-voltage direct current (HVDC), motor drives, and battery energy storage systems (BESS). The expanding uses of the MLI have lead to creation of new topologies for different applications. However, one of the disadvantages of using MLIs is their complexity. MLIs consist of a large number of switching devices, which can result in a reduction of system reliability. There are significant challenges to the design of a reliable system that has the MLI’s capability with integrated fault-tolerance. In other words, design a system that can handle the fault, totally or partially, while maintaining high power capabilities and efficiency.

This aim of this dissertation is to investigate the fault-tolerance of MLIs from two different points of view:

1. - Develop new solutions for existing MLI topologies. In other words, add some features to existing MLIs to improve their reliability when a fault occurs.
2. - Design new MLIs that have a fault-tolerant capability.

A new open-circuit fault detection is proposed in this dissertation. The new fault detection method is based on monitoring the output voltage of each cell and leg voltage polarity along with each switch state. By monitoring each cell output voltage and leg voltage, the faulty cell can be detected and isolated.

A novel circuit to maintain system operation under the condition of one (or more) components suffering from a faulted condition is also proposed in this dissertation. This results in a topology that continues to operate at full capability.

Additionally, a new topology is proposed that offers reducing the number of batteries by 50%. Also, it has the ability to operate under non-unity power factor, which enables it to be suitable for battery energy storage systems, and static compensator (STATCOM) applications.

Another novel hybrid cascaded H-bridge (CHB), known as the X-CHB, for a fault-tolerant operation is proposed in this dissertation. It ensures seamless operation of the system under an open/short circuit switching fault or dc supply fault.