What Led to Success in Academic Research on the Family of Modular Multilevel Cascade Converters?

This paper provides a comprehensive discussion on the topology and terminology of the family of modular multilevel cascade converters, including their chronological review. It is followed by answering the following question: "What motivated the author to apply phase-shifted-carrier PWM to the multilevel converters?" The PWM is achievable from integrating inter-cluster balancing or inter-arm balancing control into the middle layer of a hierarchical control system consisting of three layers. This integration makes it easy to expand the phase-shifted-carrier PWM to any bridge-cell or chopper-cell count per cluster or arm.