Floating capacitor voltage regulation in diode clamped hybrid multilevel converters

The family of hybrid topologies consisting primarily of a main neutral point clamped (NPC) 3-phase inverter followed by one or more series connected H-bridges in each output phase show promise in medium voltage applications requiring high power quality and minimal size and weight. Another distinct advantage of this topology is the ability to supply the main NPC converter with a single independent fixed or variable DC source if floating capacitors are used in the series connected H-bridge inverters. A new method is proposed for regulating floating capacitor voltages in the series connected H-bridge inverters. The proposed method provides independent control of each capacitor by decoupling floating capacitor voltage regulation of a particular capacitor from all other floating capacitors within the converter.