Hierarchical Control of Modular and Scalable Power Converters based on Multilevel NPC Topologies

This paper proposes a novel hierarchical control, which is integrated into a modular and scalable power converter design approach based on multilevel neutral-point-clamped (NPC) topologies. The proposed control of the system is structured into three hierarchical levels associated to the three hierarchical power hardware modules conforming the converter architecture: the primary control at the switching cell level, the secondary control at the converter leg level, and the tertiary control at the full converter level. The paper also defines the interfacing input/output information between controllers and the controller tasks. The proposed hierarchical control has been successfully implemented on a prototype of a three-level three-phase active NPC converter leg. The experimental results demonstrate that the interconnected controllers at each hierarchical level operate synchronously to guarantee the desired functional performance and, in addition, operate to balance the temperatures across the modules of converter leg. The proposed hierarchical control facilitates and simplifies the reliable control implementation of complex systems, by decomposing the global control into smaller control tasks at different modules and hierarchical levels. Consequently, it enables the easy implementation of sophisticated controls in a methodical and reliable manner.